Your mom was probably going to be the better choice between her and your older sister, and the thought of going to a friends house sounded even less appealing seeing as you could be spotted on the way and there were no guarantees that your friends would react favorably to the new you. While your mother probably wouldn't welcome seeing a massive, multi-headed snake in her house, she was less likely to scream bloody murder when she saw you and would probably be willing to listen to what you had to say. She could also be helpful in convincing your older sister to come around and not see you as a massive killer snake but as her brother. You would have rather started to reveal the new you with your little sister seeing as she was just as much in love with snakes as you, but unfortunately, she was having a sleepover with a friend and wouldn't be home till your mom went to pick her up at around 10:00.
You began to try to move your new body, but with how different it was to what you were used to, it took you some time to get a hang on what to do. You had studied how snakes moved and were trying to figure out how this would work for you. You were able to get a hold of how your body bent, a feeling indescribably strange given that you could now bend it back on itself several times, and eventually figured out through trial and error that the easiest way for you to move yourself forward would either be by rectilinear locomotion or by extending your first ten or so feet of length after where your five necks connected to your body forward and then using that to help drag the rest of your body. You had tried a serpentine motion but the amount of coordination that it required was too much for now.
Fortunately for you, the more you tried, the easier it became. After maybe half an hour of practice, you were able to move as if you had been doing this all your life. The transformation had probably also given you some instincts that made learning how to use and live with this body easier. But the one thing you had yet to fully get used to were the four additional heads. If you didn't focus on controlling all of them at once, they tended to start doing their own thing. It wasn't anything you wouldn't do yourself, looking around the room, watching the rest of your body as it moved to make sure you were doing it right, occasionally tasting the air with their tongues to examine the surroundings and see if you had gained that sense. But the strange feeling of doing several things simultaneously, most of which were done without even really thinking about it, was something you knew you would just have to get used to.
When you finally felt comfortable in your new body and ready to meet with your mom you began to slither over to the door to your room that leads to the hallway. When you reached the door, a task that didn't even require you to move your entire body given your new size, you were faced with a new problem, opening it. You were thinking over how you were going to open it when the thought came to you to just bite the handle and pull down seeing as your door had a lever handle and not an actual doorknob. No sooner had the idea come to you then one of your heads reached out and did just that without you even having to tell it to do so.
The door opened without a problem and you were greeted to the sight of your house's upstairs hallway. When one of your heads flicks out their tongue you were bombarded with the scents of the rest of your family. You began to slither your way over to your mother's room, finding the feeling of being both in your room and in the hallway remarkably strange. When you arrived at the door to your mother's room you reached towards the handle with one of your heads, only to stop as you felt the back of your tail suddenly fall and cause a loud thump to resonate throughout the house as it landed on the ground.
You froze for several seconds, waiting to hear if either your sister or mother were woken up from the sound. After several seconds of hearing nothing, you turned one of your heads back towards where you and your older sister's rooms were. Looking back, you saw that despite having extended your body all the way from your room to your mother's, you could tell from how thick your body was that was coming out of your room that there was still a sizable portion of yourself still in the room. You figured that as you were extending yourself, a portion of your tail that had still been on your bed had slipped off.
When you felt that the back portion of you falling off of the bed hadn't woken up your family, you proceeded to open the door to your mother's room and slither in. Not wanting to risk your sister seeing your massive length and mistaking it for a wild and dangerous snake, you begin to pull yourself into the room, it took around thirty seconds for your entire mass to be brought into the room, but when the end of your tail finally made it into the room, you pushed the door closed with one of your heads and moved over to your moms bed.
Now, all that was left was to figure out how you were going to approach telling your mom you were now a massive, five-headed snake.