ᐅ Touching up the recessed area in the exterior plaster/render

For our house (wood frame + prefab with external insulation system), openings were left at the bottom area around the front doors to install the block steps and entrance platforms. These have now been installed, but the openings were quite generous, so there are still gaps on the left and right sides at the bottom of the front door. How should these be filled? The waterproof membrane and vapor barrier are in place.

I was thinking of filling the gaps with mortar/cement and then applying the exterior plaster to blend it in?