Hi, im19 & ive always wanted to have children.my vagina (the exterior) is extremely small, the length is 3cm (entire thing) i dont know how a baby would be born from there. am i able to do a natural pregnancy? would there be complications?

This is something you need to ask an OBGYN after a full evaluation. There are rare women whose reproductive parts did not fully form or formed differently. If you have natural menses your system may have enough of the right parts to carry a pregnancy but you should have studies to verify things are okay. What you believe is small may be within the range of normal.