Baby in 90%

Today, I went to the Dr. for an ultrasound at 19 weeks.  She told me my baby's size is in the 90th percentile. I was kind of shocked because I don't feel big and I also wanted to keep this 3rd pregnancy baby at good size for delivery. 
My last baby was 8.2oz and I am only 4'11" 100lbs. I had to have a c-section with her, due to her size in comparison to mine. 
I was hoping to have a VBAC (vaginal birth after cesarean) with this pregnancy. After this news today, I am a little worried. My first baby was 6.10lbs vaginal delivery and I gained 30 lbs. Second pregnancy I gained 35lbs. So far with this pregnancy I have only gained 5lbs. 
What can I do to help me deliver vaginally? 
Any advice or comments are welcome.