Are there are any foods which help you to put on weight on your backside?

Unfortunately, there are no " foods". Most food you eat will go to your stomach first, which you don't want. The best way to a rounder is to do some squats with moderate weight so that your will sit out firmer and ier. Since you are in a rush, do them about three times a week. (mon, wed, fri ) About three sets of 20 reps will help. Peace and love.