The maximum for my college supplement is 250 words and I’m currently at 213 words. Is that enough?
Quality is better than quantity.
Exactly like skieurope said. Have you made all of the points you want to make? Is it clear and easy to understand? Does it uniquely show who you are? Does it answer the supplemental prompt/satisfy what the admissions people are looking for? If those questions are answered sufficiently, then being just short of the word limit shouldn’t hurt.