Need help from Rock n Play Sleeper to crib!

knightbaby

DS (9 weeks) has always liked to sleep in his Fisher Price RnP Sleeper and hated lying flat (crib or Pack n Play). My doc said it was fine to let him so we have. 

He starts day care full time in two weeks and will have to nap in a crib. Whenever I put him in his crib, his arms and legs flail about and he cries! What have we done?!

 Does anyone have any ideas? 

Thanks so much!