Don't get discouraged! Keep riding consistently and, if it's possible, add in some strength training. If you're not sure how, a good place to start is the weight machines at your local health club. Almost all clubs will give you a free orientation where they'll show you how to use all of them and give you some basic recommendations. If you go through the whole circuit a couple of times a week and continue to challenge yourself by adding some weight as you get stronger, you'll see changes in the firmness of the muscles underneath the saggy parts you hate!