I second the idea to open a couple carefully (say, over the sink). Make sure they are good and cold. Warm beer will foam out of the bottle many times.
I feel like you're fine, though. I started out with a MrBeer kit with plastic bottles, and even though they were thick "soda" style bottles, even they would bulge some and the indentions in the bottom would flatten out. It's a fine place to start but I got away from plastic bottles as quick as I could. They just don't seem to work that well.