tummy time at 4 months!

My little guy just turned 4 months and I feel he is still behind on his tummy time skills...he lifts his head and turns it from side to side and only lifts it high when he is pushing up with one arm. He will not push up with both arms yet. We go to the pediatrician tomorrow so I'm going to ask. Anyone else in this same boat? He holds his head up fine and can lift it up when flat on his back too!