I wish they'd use longer names for the kits so you could search for them on the forum.

The kit picture shows quite long solder tabs for the barrel jack. I think it should be possible to carefully bend the two wanted tabs sideways and cut off the unused tab. You'd probably need some heat shrink over the tabs to stop them grounding out on the pot casing, but it might just give you enough room with the barrel jack orientated in the most favourable position. You may need to thin down the longer, wider sleeve/ground tab.

If your soldering is good, then you could probably gut the tab lengths down and solder directly to the stump you've left rather than use the holes on the tabs. You may even be able to drill new holes in the shorter tab lengths.

Just make sure that if you cut off the unused 'ring' tag from the jack that you pick the right one to remove. You can get 'mono' TS barrel jacks but the kits all cone with 'stereo' TRS jacks (often used to switch battery circuits for active guitars or basses), where the R, 'Ring', connection is left unused (though it can be connected to the S, 'sleeve', connection for slightly increased reliability). I always end up having to draw a diagram and use a multimeter and a TRS to TRS lead to bell out the connections just to make sure. Those barrel jacks tend to follow a similar pattern for the connection tabs, but some arrangements can be different to that expected. It never hurts to double check.

I don't know how well the barrel jack screws against the body, but quite a few people end up making a small wedge of wood with a hole in the middle of it to glue onto the inside of the cavity so the nut and washer sit flat.