Having that small gap at the cab side helps with clearance to get the top off. The side clearance is less than 1/4" on ours...which looks just fine by me.I had noticed that most installs I’ve seen pics and videos of all had it mounted further forward, leaving that ledge on the tailgate. The cap seems to have slightly too small a footprint, both in length and width. It looks to come about 1/4-1/2” short of the bedsides as well.
Definitely looks better scooted back, but it should be flush all the way around.