Anxiety and my bf

I get anxiety really easily and I have panic attacks. It’s really difficult to explain to my bf. He doesn’t get it. For example one day it was the first day of classes for college and I was with him. We had lunch and I thought my class was at 12:30 but it was at 12. I realized this at 12:30 and he’s like it’s no big deal just walk in. And i started panicking, I couldn’t just walk in because people stare and I’d get questioned by the teacher in front of everybody. I just can’t do that. And I tried explaining it to him and he didn’t understand. He looked at me funnily and I felt so uncomfortable and ashamed. It felt like he thought I was making it up. How do I explain things better to him? Because he’s just goes for it and I have to stop and think because of my anxiety whenever we do anything.