I am going to pick up on a couple of points;
She rubs her head whilst trying to fall asleep, my solution, hold her, on your lap or in a sling, until she is asleep. That she is rubbing her head from side to side so much/fast/hard that it is making her head sore, to me this indicates a level of distress, perhaps she needs holding or rocking to sleep. I don't know why you expect a baby of 8 weeks to be able to settle off to sleep without being rocked/nursed any way!
The only safe way to have a tiny baby sleep on it's tummy is on your chest, so that you can hear and feel them breathing and make sure thier faces are not covered. Premmies in SCBU/NICU sleep prone, but they are monitored constantly.
You want to avoid flat head, well, babies from cultures that use slings don't get flat heads, and it's not a coincidence!!! Carry your baby, don't put her down, at night sleep with her next you so she sleeps on her side facing you and not flat on her back alone in a cot/moses basket.
At 8 weeks neither of mine were having "daytime naps", they both just nodded off after feeds, it sounds to me as if you are being quite rigid and structured, so I also suggest you throw away the Gna Frd book and just feed her when she's hungry, cuddle/hold her a lot and let her fall asleep when she's tired!
Just chill. With your baby and here on MN!!!