Welcome to the Jungle....
Sadly, bananas will flower and TRY to make fruit late in the season.
That is when they do this ....after a long hot summer.
Look at your plant .....like a tomato plant full of green tomatoes at the end of the season,they just will not ripen.
However your season(as well as mine) is too short for the plant to fully produce mature fruit.
I have flowers and bananas(small inedible) on a few of my plants and they will not mature because the season is over and if I wanted to continue to try to RIPEN the fruit......it is not worth the effort and cost.
On the bright side......Welcome, and have a good time cruising the forums.