wait until your af is due. if it is late then take an hpt. if it's not late then you're probably not pregnant. don't stress though as that can cause it to be late as well. just try to relax and not think about it. i know it's hard but the more you stress the more likely it is you'll end up late anyways. so just wait then test.
and yes you can become pregnant from pre-ejaculate.
Yes, you could get pregnant. Pre-ejaculatory fluid contains some sperm. If you're rally concerned, then wait two weeks and take a pregnancy test. Although IMHO if you don't have your facts straight your not ready to b having sex at all.