You won't gain THAT much muscle mass by lifting
weights. If it were that easy, we'd all be ripped. You should lift
weights because your
body burns more
calories simply by having muscle to maintain. It requires more
energy than maintaining the same amount of
fat, so you create more of a calorie deficit.
There isn't really anything you can do unfortunately. People's bodies lose weight in different places based on genetics and what they do. I lose it in my
abs pretty easily (lucky me) but god forbid my thighs get thinner. Try running or taking a class that emphasizes twisting or other core aerobic work if you want that midsection to go away.