Lost changes to drawing

Just recently started using free version. I am planning on writing a construction book and want to illustrate it myself. I do plan on buying either the shop or pro version as soon as funds available. Couple of questions: where did my changes to a drawing go? I started on a drawing at home and made advancements on it at my girlfriends, then when I got back home the changes were gone from my account. I thought they were saved to a cloud? Are there bugs in web that may lose work done to a project ( that was 3 hours lost) Secondly: Are my efforts going to be in vain once i do upgrade to a payed version (can’t use the work in free version for a book being commercial) Will I be able to access my drawings that i do now in a payed version from the free version?
Thank you for your time and consideration

In the free version, where do your sketches end up. If there is a way to save it on the computer instead of the web you should be able to edited it.