Pregnancy weight.

Hi. I've always been naturally thin and was wondering how do I keep from gaining unnecessary amounts of weight. As its a myth the eating for two. Now I do eat fruit and veg but I crave highly fatty things that I know will leave me huge after birth. I am not active never have been lol even worse now I'm preg (10 wks today) has anyone else had the same worry? I really don't want to be left with lots of weight. To be fair I do give in and eat pizza, lasagna etc haha does anyone firmly refuse to give in or what do you eat instead xx