Which boat does this sail fit?

I think you're going to have a tough time getting a response based solely on sail dimensions. For example, my boat is a Dart 18 but my sails are smaller than the average 18 ft boat. I recommend you post pictures of any logos on the sails.

Based upon the information above, I'd vote for either a very small main (14/15 ft boat) or a very large jib (off a much larger boat).

Go here
https://schrs.com/ratings.php
Do not view on mobile device or you will not see the entire worksheet. View on computer. Compare the luff lengths to see which boats match. If you know your sails area, even better.