First of all: the game is completed.
The park event is complete? The guy always ask for a better dress but i can walk outside only with the teacher outfit.
You should have the skirt suit. Try to wear that. If this is not sufficient, go to the shop in town (above your home, normal world) and buy everything there. After that, Serena will say something and you can ask your friend in school (teacher) for another shop - she'll join you in the afternoon then.
Also: Learn passive skills at Eve like "reduce shame 1-3", panties off (if accessible) and stuff to be able to move around more freely and without (parts of) your underwear. Then revisit the park.
Is the christmas party a one-shot event? I don't see the circle anymore in the changing classroom.
Christmas Party is pretty short afaik. You can get some scenes due to how drunk Serena is. But you should be able to access it more often. Probably you should try to undress or wear your christmas-band in the classroom to access the circle again.
I remember that the succubus gave me a quest to search for containment sigils in the magic world, but i can't find them.
Unfortunately I don't understand what you mean by that :/ Sorry!
