First practice ever!

Help! I'm going to my first practice ever for a master's swim team on Sunday morning. I've been swimming on my own since March and have worked up to 50 minute sessions-a little over a mile-3 days a week. I've never been coached or trained before, so the whole thing has me pretty intimidated. I've been reading the forum and from what I see, you all seem to recommend team training to improve. I'm over 40, still about 10 pounds heavier than I'd like to be but not in horrible shape. I'm a little nervous that I won't be able to keep up or that people will resent a slow untrained swimmer messing up their practice. Any advice? Thanks!!