The ab lounge will not make you slimmer, but it will help to strengthen your abd to some extent. Keep doing the cardio, but the BIGGEST factor is a clean diet or you may see no weight loss at all. If you are doing the cardio AND have a clean, low calorie diet, then you should see some results within a couple of weeks usually.
Holding in your stomach during exercise (running/walking) is ill advised. Not getting that full-belly breath is part of what can cause side stitches. However for the rest of the day, if you can, hold your abs tight. It will help your posture, for one, and if you train your ab muscles to hold your body up that way, it will make you look leaner instead of having a Buddha belly.