Checking

Make sure that your edge is both circular and level.

Check that the edging strip is level by using a spirit level along a straight edge, tapping down the edge where necessary. For a perfect circle, check the diameter measurements and reposition the edge as necessary.

Drive in more stakes around the edge and fix more strips of plywood to the stakes. You will probably need shorter stakes than the earlier stage, as you will now have less room to manouvre, and the stakes have to go in the right place first time. So you don't want the risk of not being able to drive them fully home in the place you want them.

Getting the your edging strip absolutely spot-on is well worth the time and trouble so don't rush this stage.