Which measurements are over? Your fundal height (tummy)? If so they will just want to get a more accurate measurement of baby, make sure he/she isn't growing too rapidly and also to probably check amniotic fluid levels...One or both of which can give a larger than expected fundal height reading.
Don't worry too much, fundal height isn't an accurate science by any means. There are many variables with it, for example you could've just eaten so had a full tummy, you could've had a full bladder or had wind/gas that can push everything up and lead to a bigger measurement. Even human error. Ive just had the opposite problem, had a low tummy measurement last week at 36wks (I measured 32) I had a scan booked for Monday anyway and I was super nervous. I went along and my baby is measuring perfect, in fact a week bigger than my dates. They're just being cautious and look at it this way - you get to see your baby again before birth, that's always good lol. Best wishes :)