Doc says boy but.....

So today I went in for my appointment and she told me I was a month early for it and that she can do measurements, so I asked is there anyway you can try to see the gender of my baby? I am 16 weeks and I know people Find out as early as 14. She says she thinks it's a boy but don't go out to buy anything yet. Is this because sometimes it can change later? Here's some pictures