Can people download my art from my website?

Yes, but they can't make prints from the images because the images are low resolution. You could barely make a print the size of a postage stamp with a download file from a website.

Do not disable right clicking, it only serves to hinder your sales. People might want to right click, download and save the image to show it to someone, that's a good thing.

Are you worried that someone might copy it? They could just leave it up on their computer screen anyway.

Your work is your work, it isn't legal for anyone to copy it anymore than you could copy a book and sell it as yours.