Why won't my school compromise?

I'm a freshman in high school in Texas that has year round schooling. So I'm like NEVER in trouble at school at all (I'm actually an honors student) but this morning I let my friends peer pressure me into joining them in bullying a girl during PE class, and we totally got caught. I felt bad about it as soon as I did it and I HAVE apologized. I know it was wrong. But the school isn't cutting me ANY slack even though I have a great track record. I got sent home early with a form informing my mom what I did (totally fair) and that I will be getting swats tomorrow. I just think this is a gross overreaction. I've never even had detention but once! I haven't given my mom the letter yet, though I know I need to when she gets off work today. I'm not saying I shouldn't be punished at all, its just that swats seems so extreme. I just don't know why I can't get a little slack?