That is understandable! Depending on what writing program you use, maybe setting the margin while writing will help you see when the paragraph becomes too long. I usually just put 3~5 sentence per paragraph depending on its length. Sometimes only 2 sentences and occasionally one sentence lol.
Best of luck on the contest!
PS: If you plan to get contracted, I advise you to read 3-5 times, understand the terms and everything so that you won't be troubled in the future.
PPS: This is only my personal opinion but WN contract is horrible for creators who wished to do more for their work (such as creating spin-offs, sequels, comics, audiobooks, etc etc). So read it several times or consult a professional if you have to. On another note, if you don't mind the terms, you can just sign away your work (literally sign them away by giving all your rights to WN). Contracted author have more priority when it comes to being featured.