Your banana is just showing cold damage from exposure to below 0C temperatures,nothing more and nothing to be concerned about unless it reaches mid 20sF in the garage for hours. If not,just put it back in the garage and it will be ok till spring. There was no need to cut folded leafs as although folded,they show that a good portion of them was ok and they would be at least partially functional. My Blue Java was exposed to -3C overnight plus snowstorm and close to 0C for a day and it still retains green tissue on some of its folded leafs. They don't die just because they folded
If you want overwintering to be easier on it and to start growing already,you could place a strong fluorescent light over it in your house and you wont believe how fast it will grow! But this growth will probably burn when you place it outside in the sun again.