It might be worth looking online or speaking to a school nurse or something who should be able to give you some help.
At the end of the day it's not your mums decsion about the abortion. It's your body and your baby not hers.
If you dont' want an abortion then don't let your mum make you. There are teens on here that have had abortions to please other people and found they regretted it and it wasn't the right choice for them.
If you want to keep it then keep it. You have to decide what's best for you and your baby and not let other push you into anything you don't want.