She isn't behind on her milestones, so don't worry! Babies manage to confidentially hold their heads up closer to 6 months. My baby girl could by 5.5 months. I did tummy time with her maybe 5 times with her on the floor because she hated it. Being on my chest and looking over my shoulder was what she loved or having her back to my tummy and walking around the house showing her outside etc was great. As someone once told me and it helped me relax. "You don't see adults walking around unable to hold their heads up because they didn't do enough tummy time." Also as my mum pointed out, tummy time wasn't a thing when she was having kids and we all learned to hold our heads up. You are doing great! X
I was in your shoes once mama, my LG HATED tummy time and I was obsessed with thinking it would have long term effects if I didn't do it. As others have said, holding your baby on your tummy, over your shoulder counts just as much đź’š
Try not to stress, though I know that’s easier said than done! It sounds like what you’re doing is excellent. She will get there.