Keep your body safe in the chance that you are pregnant (don't drink!!) until you know. Really, the only way to make the stress go away is to take that test and find out for sure. If you are pregnant, you have many options. Talk to someone trusted about your options (abortion, adoption, keeping the baby).
You should really look into birth control or condoms. I know withdraw might be the easiest for you right now, but it is also MUCH more dangerous. You can pick up condoms at any drug store. You can get birth control and condoms for FREE at planned parenthood if you are in the US, or at your local clinic. Some schools even give them out for free.
If you are that worried about pregnancy, then you need to protect yourself a lot better.
but TEST! You won't stop worrying until then! Go out and get one now if you can