I should really attempt to make my own Gravity Falls self(most likely it will counter this picture with my pessimistic attitude lol), but ALAS, look at all the pictures I have in my DeviantArt page. Using Paint/Paint.Net is harder then you think.
Paint programs may seem hard to use at first, but all it takes is a bit of practice! (Cliché but true) I used paint for a while and even though your tools may seem a little limited compared to programs like Photoshop, you can still produce really nice works of art! You can do it, I believe in you!