When you export a wall its height will include the floor thickness, that's why your exported wall is higher than 60 cm. Use the bottom level to avoid the added floor thickness and make the wall height 1mm less than what you need it to be (the system adds 1mm).

Since a few weeks there is a better option for what you want: the panel-with-a-hole generator on dodecagon.nl. See this topic for more info: https://www.sweethome3d.com/support/for ... read,13936
You set the dimensions you want for the countertop and the size and position of the hole. After you generated the object you can download and import it. Of course you can set a texture on it. Check it out here .