Ah, don't worry too much, this is quite common actually! My neighbour had a similar situation where baby's head was measuring ahead by a couple of weeks, tapi perut dia on track macam yours, and doc said it's just normal variation, some babies inherit bigger heads from one side of the family, kan. Sebab the abdominal measurement is tracking properly at 28 weeks, that's the reassuring part. I've heard from a few mums that this happens quite a bit, and their babies turned out absolutely fine and perfectly healthy.
That said, it's always best to follow up with your doctor at the next scan to monitor the trend, they'll want to make sure everything stays proportionate and there's nothing else going on. But honestly, from what I've seen around, isolated head measurements being a bit ahead while belly is on track usually isn't something to stress over. Wishing you a smooth rest of your pregnancy!
Nur Syafika