Don't worry too much about "if it's good enough". Even if you don't win the contest, the fact of participating has also other benefits :)
You discover other artists, other artists discover you, you make new friends, and especially, you go out of your comfort zone which makes you discover new things, try, learn and progress.
Most of the contests ask you to create something new specifically for the contest. I like this a lot because it's each time a source of inspiration for me and trying each time to do a bit better. (for example I'm still rather new in watercolor and I never ever drew a bull before, but now I did it! :) I see this as an exercise and a relaxing moment!)

And if you are amongst the winners, that is of course the top!

Have fun!