Re: Am I doing something wrong?
From my experience, the change in diet is the number one influence in my weight loss and maintenance. With exercise speeding up the process, and making it easier to maintain. I would have to say that as long as you're eating enough so that your body doesn't think it's starving, you should start seeing some substantial results.
Your weight goal is probably fine. It might be too low if you really pack on the muscle, and will also depend on your build. You might actually end up at your high weight, but with more muscles and less fat. And that would be okay too.
My cardio goal is about the same as yours. With nicer weather, I usually increase it a bit. I think your 3 days of cardio is a good goal. A person doesn't always have the time for more. 3 times is a heck of a lot more than what you used to do and you're not trying to lose a lot of weight.
From my experience, give you self a lot more time for the weight loss than what most people expect. You could easily lose the weight in two months, but give yourself more time. ie. at least a few 5 months. Now many people would scoff at taking 5 months to lose 20 pounds, but by doing it a slow rate, your body will have time to adapt to the new you. ie. exercise and less junk food. Maybe you won't be exactly where you want to be by summer, but you for sure will be there next summer. Because by next summer, you'll have more than a year of your new lifestyle under you belt (and not over your belt).
I used to have a real addiction to pizza, potato chips, etc... Still eat pizza, but I eat less of it and make sure I enjoy every little bit. No more wolfing down the food so fast that I don't even know I ate it. I'm not going to give up and meal-time type of food, but I'm also going to eat reasonble portions when I do.
I don't know anything about any type of supplements. I most cases, I don't think they're necassary, but I'm sure many would disagree with me.
Anyhow, good luck. If you get this figured out at your age, in 20 years, you'll still be able to see your toes.