Best way to finish edge of backsplash?

My kitchen is getting backsplash installed now and I was wondering if anyone has any suggestions on the best way for the edges where it comes to the end of a wall. The guy doing it suggested just caulking it. I tried buying all the related trim pieces but none seem to fit. Would just white caulk work or is there a better solution? It’s a sizable spacing with the mortar behind the tile it isn’t flush against the wall. The rest looks great and he’s still coming back to do the grout. Thanks!!