If you and your boyfriend used a condom, and used it correctly, chances are your likely not preg. Condoms are like 99.9% effective when used correcty, even if he doesn't pull out. I remember when I was younger, every time I had sex, I would always worry about it afterwards until I got my rag.
It is just your insecerity, and uncertainy stressing you out. Your only 16, and what if....... Don't worry about it, wait like a couple of weeks, and got get a test.
A stop having sex if it freaks you out that much!!
Good luck