My hidden journey as a new Muslim and my salah struggles

Assalamu alaikum, everyone. My mother found my prayer mat that I ordered online, and it led to a really harsh scolding. I won’t go into details, but it was pretty upsetting. Now I’m scared to pray if she’s around and awake. Alhamdulillah, she often sleeps after work, so I manage most prayers. But that’s the issue-I can’t always do them. My routine is to pray Fajr, then when I come home from school, I combine Zuhr and Asr. But sometimes, she stays up and I miss both because I’m terrified of her reaction if she catches me. I can’t pray Zuhr at school either, because if people find out, it’ll reach her eventually. I wonder: is my Zuhr valid if I pray it with Asr, or any missed prayer I make up later? About hijab, I clearly can’t wear it full-time now. I just use a scarf as a temporary hijab during salah. Am I sinning for not wearing it outside? I’m also keeping my faith quiet in public. There are parent-teacher meetings sometimes, and my teacher might mention I’m Muslim. I’m in a mostly Christian country, and at school, they teach the Bible and do Christian prayers in class. I stand respectfully but don’t make the cross or bow my head, focusing my thoughts on Allah. The students take turns leading prayer, and soon it’ll be mine. I could use general words like ‘God’ without naming Jesus or Allah specifically, just a neutral prayer so everyone can follow their own beliefs. Any advice?