Calling out

My job takes advantage of me badly bc im naive and shy and I want to call out next friday just to screw them over lol. ok well that’s not the only reason, I made plans w my bf. my manager lets everyone have days off except for me and one another person and it’s just not fair. they made me come in WITH COVID one time while I had a fever and suffering. so yea it would be nice to put myself first for once and just call out since I never do. i have calling out anxiety and feel guilty and my boss knows this so she uses it to her advantage. (i am looking to switch jobs btw) but anyways, what’s a good excuse??