HEy Mummymeg,
I can see what youre talking about, but its not too bad. Theres been some great suggestions here too. My dd was in a hip harness for 6.5months and developed a very flat head. She also only turned to one side. Physio got us to approach her from the other side and also to put her toys on the less favoured side. It only took a few weeks to start getting her to looking in the other direction. Also tummy time and sitting up when she has more head control. Shes only 2 months, so you have plenty of time to get it rounder. DD is now 15 months and her fontenelle is still open a bit, so there is still more room for her head to round out. Its so much better than what it was in November.
Good luck