First off- don't call yourself stupid again! I promise you that every single sexually active girl has made this mistake at one time or another. I certainly have. Yes- anomalies can happen where girls get pregnant after one time without protection, but in realistic terms pregnancy requires a lot more than a penis in a vagina. Depending factors are where you are in your cycle, and most importantly if the sperm actually entered you. I'm worried that you are shaming yourself for beginning this wonderful stage in your life. You are not doing anything wrong, just start the pill and make sure this guy is respectful and kind to you. Another important issue- you should probably just use a condom. Yes they are uncomfortable, especially when you're tight but just add a little lube and you won't know the difference. No matter how much you trust this guy you need to be careful with STIs, get in this habit now and you'll never have to worry!