It's highly possible that in reality you have a very good memory, like most of people. For example if you're a programmer you probably remember hundreds of API calls, syntax features for various languages, keyboard shortcuts and so on.

I always taught myself that I have terrible memory but then I realized that it's not terrible - it's selective. We have so much information coming at us every day that our brains have to make choices what to remember and what to forget in few minutes. The problem is how to make them cooperate and actually remember stuff that we want :). I found that if I really want to remember something there are two things required - repetition and connecting it with something I already do remember.