26 weeks 6 days baby on small side

I had my tummy measured today & the doctor said I’m in the normal range but baby measuring on the smaller side. Is he likely to have a growth spurt? Is there anything you can do to help him grow more? I eat fairly well, drink lots of water & limit myself to 1 coffee a day, no drinking/smoking, walk half an hour most days? Not sure what else I can do. I am a petite person & my husband is 6 ft 2/3.