When painting countertops, you can find streaks and marks in the topcoat varnish occur for a few reasons. A new roller needs to be used for the varnish. An adequate amount of product needs to be loaded onto the roller. The varnish is then applied in a single coat and can not be re-worked with the roller once it has been laid. The product is self-levelling and if you try to add more or go over the area once the coating has started to cure this is when you will start to see streaking.
In summary, load a new roller with plenty of topcoat, apply the topcoat to the bench in even passes with consistent light pressure and then leave it to cure. Do not go back over the area once you have laid a coating on it.
You should wait until the next day after painting the benchtop before applying the clear topcoat.
This step-by-step tutorial should also be helpful: How to paint a kitchen benchtop. - MitchellMc
