Here is a good post***see edit below***, with sources, on canning bananas safely. I haven't tried it personally, but it's a page that I have bookmarked in my preserving tab. They definitely recommend pressure canning, not water bath, due to the low acidity of bananas, which is obviously what you did. It's always a wonderful thing when we can obtain a food at a great price in bulk and preserve it to eat at our leisure!
I don't know if you've made fruit leather, but I love to mix a mashed banana or two in a batch with another fruit - I've done it with raspberry, cherry and blueberry fruit leathers, and they add a nice subtle flavor and I think improve the texture as well!
edited to add*****
I had that page bookmarked - but I just followed the links they provided, and neither link actually had any recommendations at all on canning bananas, so I think the writer extrapolated recipes from other types of fruit. I would have researched this thoroughly before trying - so I apologize for recommending the page. I will (for myself) definitely do a lot more research and find a tested recipe before ever attempting to can bananas. I would probably freeze, dry or make fruit leather with it before I would can bananas without seeing a properly documented tested recipe. I do know that there are many people who do things that aren't tested first and are just fine (think canning cakes! yum), but I like to fall into the better safe than sorry camp.
If anyone knows of a link to such a tested recipe, I would surely love to see it!
