Sperm will naturally come out of your body after sex. Something with gravity and it's a fluid. You can help to not move after intercourse for about 5 minutes. I've heard others that have done this say it helped them. (Never personally had to do it though)
All it takes is one out of all those millions to make a baby. You can always prop yourself up with a pillow afterwards to let as much get to it's destination as possible...Good luck :D
some will come out not all of it lay on your back when fu an after its done lay there 15 min to give them time to travel up there