Aih, don't worry too much lah, lots of babies have slightly bigger head measurement at 28 weeks and it's usually nothing serious, especially kalau baby's growth otherwise normal. A few of my mum friends were in the same boat and their repeat scans came back fine, so the 2-week check should give you clearer picture je. But honestly, the best thing is to discuss this with your doctor when you go for the repeat scan, dia will monitor growth progress and explain what it means for your baby, so you'll feel more reassured lah!