I’ve attended one of those events prior, and I was not pressured to buy, but I don’t know if it’s the same for all events. You will have an opportunity to see pieces that simply aren’t in the boutique and even get to try them on. It’s a very lovely event, and if some of the pieces are in your price range, even better.
If you clearly state that you’re there to see what you might want in the future, I think that’s fair. Did you ask your SA to send you the jewelry selections that will be part of the event? Usually they will send it beforehand.