I'm really sorry to hear that. I hope it's all just a false alarm. It's good that you got SN, but living with your parents doesn't sound good for the plan. What if your parents found you before the SN took effect? For example, if you took SN and started to vomit, your parents would be alerted. Or if the SN didn't work for some reason and your parents found you unconscious but not dead. If your parents went to a vacation, or to a summer cottage, or to visit a relative, something that would make them be away for a week, that would be the time to buy and take SN. I'd suggest moving out, but of course if you're in a very bad situation already, it's hard to move out. I hope your plan with SN succeeds. You might want to rent a hotel or motel room though, if you have enough money.
I don't know if that means that it has just arrived somewhere in the UK, but let's hope so. Though if your parents see the packet, it's good to have an explanation. Manga or anime dvds or something. Or gamer bathwater. That would resemble SN container's shape.
While people may want to see your body be alive, if you'd rather have your body be dead, it should be your and only your decision. Your body, your choice. You didn't ask to be born. You should have the right to go back.
I hope all is just false alarm and that all goes well.