So, yesterday I received an offer.

I´m not gonna take, but I also didn´t reply to them.

So, when you received your admissions letters, did you answer to all Schools and what did you say?

Should I wait for the deadline to answer?

=)

If you are clearly not going to take the offer, then politely decline while thanking them for their consideration. Do it immediately. The place they hold open for you, can then be given to someone else.

Quite likely there is someone at that school on a wait list to get in. Why take up a spot that could be for their "dream univesity" so to speak? So the sooner you decline, the better is it for others.