If I understand correctly, you have already talked to your mom and she has set you up with a doctor's appointment? If you are this scared the best thing you can do, is pick up an at home pregnancy test or if you are near clinic, go there for one. It will give you some piece of mind. Otherwise just try to hang on until your appointment. Pregnancy test are routine when beginning birth control.
In the event that you are pregnant, there are options. Keep open communication between you and your mom. She will be upset and angry, but she is your mom and I am sure she loves you. Just try to keep calm and learn from this. If you aren't pregnant count your blessings and stop messing around. You have your whole life ahead of you, no sex is worth risking your happiness for. If your bf loves you, he'll understand.
Best luck sweetie. I really hope everything works out.