If the outlines weren't cut all the you can use an x-acto knife to cut out the PCBs. Just follow the contour of the outline and be careful. There might be some excess copper on the edges that can be shaved off using the edge of an x-acto blade. If the holes were no fully drilled out, use a needle to poke them out. You may want to do this over a waste bin, again to catch any dust. Use alcohol to wipe off any grime from the adhesive. Drying with a paper towel is OK but might leave behind paper fibers. Use a scotch brite pad to lightly sand away any frizzy bits.
To prevent the copper layers from rusting due to oxidation, you can optionally apply UV curable solder mask to the surfaces. We have a learn guide on how to do just that! There's other options such as coating the surface with protective sprays.