Was i wrong to get mad at my friend over this? (kinda long but easy read) please help?

No, its not bad to be mad at her for saying that. shes your friend and she should definitely encourage you to try hard at it! At the very least she could say not to be disappointed if you dont get an A+ because it's hard, which it is. But its definitely not impossible if you try really hard to do an amazing job! Tell her that it upset you because people doubt you a lot, and you'd really appreciate it if she would support you. Best of luck, i know you can do it!