Nicci,
Everytime I went for a scan my two were measuring way above normal, Twin 1 was always on about the 98% and Twin 2 above 80%, and the consultant joked I would have 2 x 9lb babies if I went to term - which petrified me, especially because I seemed to be all 'bump' and was scared they would tear my stomach muscles or crack a rib (neither of these happened). In the end they arrived at 35+5 and weighed 5lb4oz and 6lb4oz, so both really good weights and I suspect they would have been a lot bigger if I had gone to term. I was just happy they were on the healthy size and I was not worrying about them being too small!
So, in my experience, I would not worry too much. Also I did not have gestational diabetes, or any other problems in my pregnancy at all.
Hope this helps and I hope your test on Friday went well.
Jan
xx