Your picture didn’t post. Here are some instructions which should help:
Hopefully it the problem knitting pattern picture I did comes up.https://photos.google.com/photo/AF1QipMTVTafmq5RJwnnAXZ002F8Av0jY35XxXI0ACqZ
I don’t have a Google account. Blocking the coaster after you’re finished may be the best way to neaten up the corners. Are you slipping the edge stitches? That might help too.
Thanks. I have save that site. I will try that slip-knit thing first that you shown on the site.