First, relax and take a deep breath. You may find it reassuring to know that there has never been a study showing that kids who discover their parents having sex do not experience any sort of psychological damage. On the other hand, when parents do stop having sex and lose that intimate connection, it can lead to all sorts of other issues that kids can sense. Ultimately, you want your kids to grow up and be able to say yes, my parents loved each other.
Still, it's understandable that you feel uncomfortable about the prospect of getting caught. There are a few things you can do to ease your anxiety. First, install a lock on your bedroom door. If you still feel self-conscious, even with a lock, purchase a fan or a sound machine to place in front of the door or, barring that, try to have quieter sex. Change how you vocalize your pleasure. If you have a creaky bed, place some blankets and pillows down on the floor and move your sex play there.
If it still makes you uncomfortable to have sex while your kids are around, you can also experiment with changing your schedule around sex, working around their sleep schedule (especially if they're still taking naps), or even sending them out with a babysitter.
Remember: no real damage occurs when kids catch their parents being intimate. This is something that happens to all parents and, in fact, can provide a great opportunity to start talking to your kids about sex if they do by chance catch you in the act. If you create a sex-positive home environment, they'll make healthier decisions around sex as they grow older.