PDF exported from Notes is unreadable
When iOS Notes creates a PDF, it will scan the page to only print the content it needs to and not a lot of blank space. The fact that you do have a lot of blank space indicates that there is something on the right side of the page that has been drawn (maybe a small dot or line) and Notes will see it as content to be converted, giving you the large white space.

Ensure that there is absolutely no content on the right hand side of the page (use the eraser tool) and try again.