Gap in back wall to barrel

I did not specifically mortar the back wall to the edge bricks of the barrel. I figure the “oozing” of the mortar would fill some of that gapping. I assumed the blanket, stucco and brick veneer would cover whatever little gap was left. Am I good? Or is there a specific caulking I can use to fill in the gaps.

If you feel like it needs filling, here’s a short thread that details two products. (Note that we don’t have confirmation the second one does the job, but either should.) Just know it won’t fully cure until you do your curing steps.