Side roller HELP

I just put my baby in his pack and play so I could use the bathroom and make his food, I come out from the bathroom and he’s LAYING ON HIS SIDE. so first of all I’m probably going to cry and second of all now I’m terrified to put him in his bassinet tonight. We were just going to start tonight to transition out of his swaddle. I was going to do the one arm out for a few nights, then both arms out, then just a regular sleep sack. But now I’m like...which arm do I leave out? Is he going to be okay? I DONT KNOW WHAT TO DO I DONT THINK IM GOING TO BE ABLE TO SLEEP TONIGHT