It's not a shame to have skinny legs. I, myself, have skinny legs, after losing a lot of weight a few years ago; I never managed to get my legs back to the thickness they were before that, as they are probably the hardest muscles yo work out and my weakest group as well. However, it came out very helpful to have skinny legs when I started fighting as I can lift my legs up easily and really fast as well; mentioning that I am 6.1 tall and I can lift my legs higher than that. Flexibility has its part in there too, but what I mean is that you don't have to look at skinny legs like a burden, try to use them in your advantage, like I do. P.S I am glad I can wear skinny jeans.
Regarding gainign weight, it depends on your genes. If you got good genes, then perhaps your stomach will remain flat. There is one thing you can do if you want flat stomach and thick legs at the same time and that is working out your legs and running. It helps a lot, believe in me, running does.