Baby sleeping- FTM

My little girl will be 2 months on the 7th and ive noticed lately she does not want to sleep on her back. I rock her till i know shes out cold and ill put her down, shell be good for a few than will wake up and cry.. ill put her on her tummy and she will go right back to sleep. Is it okay to let her sleep on her tummy?? when she does i always make sure my eyes are on her. FTM so i freak out about everything.. im scared to let her sleep like that because she cant roll over yet a d im worried she will stop breathing.. Anyone else have this problem??