One must be very cautious when working with home based projects. Not only does a simple calculation produce a big change in the output, but it may also affect the structure for a lifetime. For instance, using excess mortars in a structure will likely cause an uneven appearance of the structure. Also, if a day or two pass away, the mortar dries up & becomes and cannot be simply plucked (or wet scrubbed) as is the case if the mortar is less than a day old.
You need to collect the necessary tools & useful safety gear. Start chipping the excess mortar from the base of the elongation. You can then start scrubbing the remaining crumpled zone with a scrubber dipped in a solution of masonry cleaner (which primarily contains the muriatic acid). Once done, allow a couple of minutes for settling & rinse thoroughly with clean water. You can repeat the process if needed.