Get 3/4 round from a tile store that matches

Was the counter professionally templated? If so, do-overs?

Have to agree with lynndowis. If this was a job by pros then they owe you a professional fit.

If that was professionally installed/cut, they messed up their measurements.

I would consider getting same countertop to have backsplash up to cabinets. Maybe 3” for sides just to hide.

Encaustic cement tiles are usually quite thick. They might cover the gap and the patterns are beautiful.

I like the option with the tiles all the way up to the bottom of the cabinet and shelves.

The left side of the counter appears to have an even larger gap which may be more difficult to hide. Any chance of a do-over?