what should I do!

Well I just woke up to check on my 3 month old son and when I looked into his crib he was on his tummy...Ive never rolled a baby over so quickly ever in my life! Somehow he managed to get from his back to his tummy while sleeping. He was totally fine and breathing bc he had his head turned to the side but I was so freaked out I could have cried and puked at the same time. Im now so scared to go back to sleep because all that's on my mind now is sids. It just scares me because he's still trying to master tummy to back. Is there anything I can do to help so he doesn't roll onto his stomach while he's sleeping or do I let him be??