Goals from Bradley Easey and Scott Floyd were not enough to prevent Steve Welsh’s side signing off with a defeat.
United finished seventh in their 10-team Midland Division, with 17 points to their credit from 18 matches.
Boston (4-3-3): Jamie Bradley; Daniel Worthington, Daniel Moulds, Joe Cain, Conor Allen; Jack Dykes (Billy Hodgkiss 25), Miles Lynch, Jack McCallum; Steven Dovey, Scott Floyd, Bradley Easey (Karolis Andriulionis 55).