I usually won’t cancel anymore (I used to)…. But I get very anxious and almost irritable about just getting there and “getting it over with”.

Funny thing is, once I’m there it’s usually ok or even fun.

No, if I commit I follow through. But anxiety prevents me from planning in the first place or causes me to say no right off the bat without giving the offer any chance. There's just something in me that convinces me that I won't like it.
On the other hand, if some other circumstances cause that the event is cancelled I sometimes feel huge relief or happiness. Suddenly I can appreciate that I can retreat to my usual activities and stereotype without fearing the possible discomforts and all the unknown.

I didn't want to admit it, but I don't want you to feel alone. I do this exact thing, too. I did it just today with my mom (who I am close to) an hour before we were gonna hang out and watch a movie. I panicked and changed my mind and decided to stay alone. its worse than that but I panicked and deleted the rest

Ugh yess

Social anxiety. Yes. But I've been better at facing it rather than canceling.

It's a kind of anticipatory anxiety and yes, it's common. I don't cancel, but I get jittery sometimes. Have you ever considered going to a therapist?