To all the 20 year olds

Hannah • Twin girls born 6/26/15
Well my fiancé and I didn't really try but we have been unprotected for 3 1/2 weeks now. I didn't temp or chart or anything but we just got lazy on the birth control and didn't care. I told my sister (childhood friend that became my cousin that my mom eventually adopted) and she was really mad at me and called me dumb and it really hurts that she won't be by my side when I find out within the next week. And now it makes me think I'm totally stupid and made a huge mistake even though at first it was an accident but we just went with it. Now I'm worried others might be the same way just because of my age and it's stressing me out. Has anyone else gone through this?