Car seat head flop

That would worry me, I’d get a new one xx

Have you tried having the newborn insert in?
I'm a certified car seat fitter and unfortunately the majority of brands are god awful when it comes to the correct fit for an infant.
You have two options really.
1. Seeing if adding the newborn insert back in makes a difference. I know brands will suggest removing at X amount of weight/height but in reality a lot of babies then suffer from head flop when their bodies are in more of a c shape due to the insert being removed.
2. Have a look at another seat from a different brand that can give you a better fit.
If you want any advice feel free to message me! Equally there are Facebook pages that will help you. Car seat safety UK allows people to post their children's weight/height and what sort of car seat they are looking for and will give you a recommendation. Just be wary though, it's an extremely toxic page where people are known to be very unkind.
I'm 100 percent on the stance that you need to do what is right for your child, budget, and circumstance.

My friends used to do this and she found the car seat and isofix weren’t quite fitted right could this be the case?

I don't think the headrest is down enough.
Put her in straight and then try the headrest down a notch