Should I meet my professors at a celebration party?
Get over your disappointment and celebrate your achievement. It's important to give yourself a pat on the back when you've done good work, no matter if it's perfect or not. If you only look at what you didn't achieve and not at what you did achieve, your motivation is going to suffer at some point.

As for your profs: If they are not total jerks, they will be very happy to celebrate with you. Nobody in their right mind is going to hold it against you that you didn't meet very high expectations, especially not on an occasion like this. You sound more disappointed than they will most likely be. In the unlikely event that someone is giving you a hard time, just turn around, grab another glass of champagne (or beer) and high-five someone nice.