my newborn won't stay on his back when sleeping!

Sarah
My 13 day old baby won't lay on his back. I swaddle him with his arms out as of 7 days because he hated his arms being strapped down. But now the second I lay him on his back he rolls to his side. I can put him on his back but he immediately rolls again.  Any thoughts on what I should do? He always has his arms out in front of him so he can't roll on his belly.