I'd like to know if there is something I can do to close the gap or hide the gap in the blinds. Obviously, I can measure properly and purchase new ones but really trying to avoid that.
I've also thought about curtains, but it's also something I'd like to avoid. Are there any solutions to this?
Here is another photo zoomed out. 
I had the same problem - the correct size blinds I bought were broken and had to return them and could only get a set that was 1 inch shorter ๐
Ended up moving the mounts slightly inward so the gaps were on the edges. The two smaller gaps on the sides were a lot less noticeable than the gap in the middle. Also ended up putting curtains up to cover the edge gaps, though it wasn't strictly necessary. I keep them pulled to the side, and they're purely decorative / to hide the edge gaps.
Moving it inward may be the way to go...
Definnetly get those mounts butt up against each other. Depending on what hardware is up in the blind track ( and it looks like the where set right with the adjusters to the outside ) you may be able to take a hack saw and trim the track just slightly like even a 1/16th off each end will end up getting that gap down an 1/8. Etc etc. Or you may be able to find a center style mount for a long single blind set up. And get the two ends in there instead of two end caps. It seems excessive BC there will always be some small gap.