I'm going to suggest a few things - I don't think you HAVE to show people your work online, but you can save it as a last resort if nothing suggested seems to work.
Often, "fragmented" writing that's hard to piece together was often written in "fragments" in the first place (ie a little bit on the train, a little bit on march the 3rd, you get the picture). It often follows the general theme but as a whole, it doesn't work too good.
For the record, I went through the EXACT same thing, hahaha... I refused to write a more appropriate ending and tacked on my 'desired' ending because I was determined to make it work. As it happened, that ending (which was largely unchanged through the whole year) ended up in every single draft... including the final one!
What I did was to sit down and plan out my writing in rough plot points to make sure that I wasn't really missing anything - sometimes as writers we're so excited about the end that we "jump" to it, or sometimes we haven't left enough clues or "planted the seeds" in the body of the story, and so the end seems out of place. You have to remember that your reader IS NOT YOU - they don't have all the background knowledge that you have. So that's why you have to leave clues for them - so they can work it out for themselves and come to the conclusion that YOU want them to.
What I personally found - and this may not be the same for you - was that I'd sort of ended up with two very similar stories that went in slightly different directions. Very very slight, but enough to sort of warrant a slightly different ending. I had my ORIGINAL ending (which I wanted to keep) but a REWORKED body of the story. They didn't mesh together that well.
It's really up to the writer to decide which one they want to change, because ultimately the story has to work as a whole. If you're really attached to your ending, try these:
* Do that sit-down thing I suggested. You might find that you just need to extend a piece in there. Write like this:
*Intro
*Main Character comes, mentions ______
*Time jump to _____ where __________ happens
-ooooh look, we need a joiner!-
* Ending
and now for the personal story. In my major work - which was quite "piece-y" to begin with - I added a second-last piece where I tied up a lot of the loose ends that had been floating around in my story. It was something that I hadn't wanted to do, but under the circumstances and with a word limit, I HAD to tie my story and ending together. By doing this, my desired ending now became a logical one (and if not logical, "natural" or "right" will work just fine too). And bingo. Success.
* Rework from the top (actually, you should be doing this anyway if you haven't already!). Cut out your end and sticky-tape it to the side of your computer. Since you'll be looking at your ending so much, you'll feel compelled to make sure the reworked stuff lays down the foundation for the ending - and thus (hopefully) the entire thing will go in one direction, ie towards the ending - god I hope I'm making sense.
Whilst I didn't go to the extreme of resorting to scissors and sticky tape personally, I did keep my ending almost perennially in mind as I was reworking (look, my ending was only about 4 lines so it was easy enough to memorise 
). I'd gotten a lot of comments that my ending seemed kind of "sudden" and "I don't quite understand...", so I wanted to plant LOTS of seeds earlier on in the story so the ending - when it finally came - would be easier to understand.
I think it's very important to remember that your story has to work as a whole - don't just change the few pages near the ending. Do the WHOLE thing - if you want it to work as a whole, you'll have to rework it as a whole
