I might be missing something obvious but there only appears to be the option to draw something in predefined places - where the bubbles appear on the map.
I'm trying to mark up somewhere new that doesn't have a bubble and I can't see how I'm supposed to do that.
Right now it's limited to ~2,000 curated panorama locations. You can only draw at existing bubbles on the map. I'm working on expanding coverage, but if you have a spot or location you'd love to see added, let me know :)