how well is your baby sitting?

Ca
My daughter was born early March and just turned 5 months. She's not so great at tummy time so we're doing it at least 2x a day now. Today a friend came over with her baby who was born in late March and her baby was sitting so much better and holding her head so much better it made me sad for my little girl. I know I shouldn't compare and every baby is different but I don't know why mine is lagging behind. Lots of people I know say they never do tummy time and never had any problem and here I am trying to be so good about it and she's still lopsided and hardly sitting. We had an evaluation with an occupational therapist because she's already getting feeding services for a cleft palate but the occupational thought she looked okay. I know I should find that reassuring but I'm just worried. She always leans to one side (we do toys on the other to try and get her to turn) and has a hard time being upright. FTM and worried!