Does your result look similar to the photos in this post?
[https://discuss.inventables.com/t/lines-in-flat-surface/28443](https://discuss.inventables.com/t/lines-in-flat-surface/28443)
If yes, look at this post. The lower part of the post is probably a fix in your situation. As Robert said your bit is probably not perpendicular to the wasteboard. Shimming it to correct is a fairly common adjustment.
https://discuss.inventables.com/t/resolved-squaring-x-carriage-front-to-back/8945/27
Searching for “Shimming Z” or Tram will yield more info.