Am I in the wrong here

I have a bf and have been dating for over a year. So I had an activity that needed to go back to school at 4 pm. I originally intended to go out at 3 pm and arrived half an hour sooner, and I told the exact same thing to him as well because he asked. But I thought he just asked for fun with no actual purpose.

But then, because I ate lunch later, I got out and arrived near school half an hour later than I originally planned.

And guess what: he has been waiting for me near school according to the time I told him, which made him wait for half an hour outside. It was meant for a surprise for me, I never knew he was going to wait for me. That is the reason I didn't tell him I got out later.

And how he is mad at me, completely ignored me and called me a bitch. I felt upset for making him wait for a long time, but I really didn't know he wanted to make a surprise for me. Idk if it sounds really childish, but am I in the wrong here?