I've gained (finally) some weight, but it's mainly on stomach. what can i do to even it out?

Weight train: If you're trying to gain weight, it should be healthy weight. Sounds like you've put on more fat than muscle. Weight training along with moderate aerobic activity and a diet rich in lean protein sources and complex carbohydrates will help you gain healthy weight.

Spot fat loss does: not occur naturally. By losing weight in general some will probably be abdominal fat. But, we don't get to choose what area of body fat is lost from. Eat healthy & be physically active. Calories burned must > those consumed. Tighten ab's: crunches, reverse crunches, exercise ball crunches, pelvic thrusts, lying leg raises, side bridge & “bicycling” exercise on back. Do regular aerobic exercise.

Exercise: You can not target an anatomic location for weight loss. You should exercise regularly to ensure that have healthy muscle mass for weight rather than fat. Have a healthy diet, exercise, drink plenty of water, have safe sex, and get HPV vaccine. Wish you good health! Nutrition: http://www.choosemyplate.gov/.