I entered my first comp after about a months of riding (back in 99)
I just had a standard xc bike, no trials mods to it at all. I was really crap, I couldnt trackstand, backhop or anything.
I entered novice and came 13th at my fist comp. Going to them really helps you to improve, at the end of the season, I was comming in the top 5 and ended up 3rd overall, I was well chuffed.
so dont worry about how good you are, just go and enter them anyway, you will get better faster.