My daughter had the same thing.
First of all...take a breath and let go of any blame or stress over it and know that she will be just fine.
My daughter's was pretty severe and still at a year, we were getting so worried. My daughters whole posture curved to the left and she wouldn't straighten her body. They suspected scholiosis...I have it.
We even had x-rays done. They pulled her straight, layed her flat and taped her head. She nearly passed out from crying and started to throw up. It was awful but she turned out to be fine. It turned out to be a leftward posture do to the muscles in her neck and shoulder being tighter on one side. It pulled her head. I did fun neck exercises with her at 4 months. (Turn to the left, turn to the right)...singing it and smiling with her. Also a chiropractor suggested mild fun swinging upside down. That would let her muscles stretch without forcing them or pulling them.
Keep doing what you're doing. Try rolling a receiving blanket under the side of her head that she is leaning to. They also have side sleeper cushions but chances are they won't do much. She' probably flip over and turn her head anyway. (Get the one with one short tummy cushion and one long back cushion...it will give her room for her arm and for her legs) I used to just sneak up to my daughter and tip her head as often as I could. Who knows if it helped but it made me feel better. She never did sleep on her belly and she never did tummy time. She hated it.
Look on line about cranial specialists and have it looked at in the 6 months because if it's a serious condition, they say it's not correctable after a year old.
It will fade as she sits and crawls and walks. And it will fade even more as she grows hair and grows up.
My daughter still has a mild spot that is flatter but so does my niece. I can't even tell with either now. Niece is 4 and my daughter is 20 mos.