I wouldn't worry too much, especially if she is only just 3 months old. We hardly did tummy time at all- Hayley will only tolerate it for a couple of minutes at a time and I was just lazy..lol. It was too hard to coordinate it when she hadn't just had a feed, otherwise she would just chuck up! Or when she was ready for bed, as she would whinge after only 30 seconds.

She is not far off 4 months and a couple of weeks ago it just kind of clicked and now she can roll over and has started pushing up on her arms. Her neck is also quite strong and she keeps straining to lift it up when she is lying down like she wants to sit up. i don't think the lack of tummy time has harmed her at all! Your bub will do it when she is ready, and as Winter said every child is different. Unless she isn't developing in other areas as well then I wouldn't be too concerned about it.