Competitions, are subjective to the palate of the judge. They have guide lines, that they follow, however, if the judge has the sniffles or has tasted several beers in front of yours, their palate can be off. If you are getting scores like 18-15 or lower, you might rethink what you have done. If not, and you and your friends like your beer, keep on keeping on!!!!!!!!
I entered a competition with a Northern English Brown. I scored a 36 and didn't even place. The biggest complaint from one judge was no esters, from the other, esters were slightly too strong. So you can see how we all have a different palate, and we all use our palate differently.
As far as entering in the wrong category, go to the BJCP style page http://www.bjcp.org/2008styles/catdex.php
From here plan your recipe based on the style guidelines, and use some of the ingredient suggestions. Plan your beer for the competition, don't just throw a beer into one, unless your are certain it will fit the style specs.