Gestational diabetes 20 wks

Hi all. I have a low bmi, healthy diet but my dad has diabetes so i was tested at about 14 wks. Only found out today at nearly 20 wks as it took that long for my next appointment I'm borderline gestational diabetes. You have to be below 8.5 i am 8.4 that was at 14 wks.. no idea what it is now.. i am very small. I only weight over 45 kg at the mo. Have gained over 3 kg so far, which isn't much. It was a bit of a shock to be honest. Midwife says if not treated it can mean a big baby and mine is in the upper weight at 20 wks. He is about 5 days ahead.. i am going to cut out my honey porridge and too much fruit.. anyone any advice on this issue or any positive outcome to it for my baby? I just want him to be healthy and i don't want this to do something wrong as so far he is healthy and all is well with development.