After a lot of trail and error I decided that the best way to ensure that these are central to the coaster was to make sure that the design is bigger than the actual coaster so that when it engraves it engraves the whole thing. This worked really well and I think give s a better effect.

Adjust the sizing so that its bigger than the material you are engraving onto. Press process

Once these are finished that's it simple to make. I did think about trying to add a top coat of resin to protect the cork but will see how hard wearing it is.