my baby was also on the smaller side in my womb, but my gynae wasn't concerned. If my gynae, with her years of experience, wasn't concerned, i decided that I shouldn't worry as well haha
I tried eating avo, durian, full cream milk, but didn't help at all. probably coz my baby was predisposed to being small. He's 5 months now and growing well, exceeded 50th percentile after a couple of months of mad drinking lol