3 month old rolling over at night

My 3 month old started rolling over tonight...i looked on him and found him on his stomach really close to the side. He's still in his pack n play was waiting for the day he could roll which i guess is today. So now im nervous changing him over to the crib. Worried first that i wont hear him when im asleep even with monitor and also worried of his rolling over. How do i keep him from rolling? I cant possible stay up all night.