Tummy time concerns

So my LO is going to be 6 months soon and she always hated tummy time but she sit up with little assistance. But during tummy time lately she been picking her head up and plops it down n lays there for like 10 seconds n gets back up and does it any over n over. I’m just wondering has anybody else have this happen. I’m scared it may be a development delay because she is 3 weeks early n was born a low birthweight. !