In your site editor, make sure you're on the SETTINGS tab, select GENERAL, scroll down, select ARCHIVE. Enter your email address and click EMAIL ARCHIVE. A link to download your zipped archive file will be mailed to you. Here's a screenshot:
NOTE: When archiving your site, be sure to use the Archive option mentioned above. It saves the theme and the content. DON'T rely on "Export Theme" in the Weebly theme editor (available when you Edit HTML/CSS) as it only saves the theme and any changes you have made to the theme itself — it doesn't save any of the content you've added to your pages.
You can't re-upload an archive in one shot to Weebly, but it's incredibly helpful and will allow you to quickly restore any part of your site that's messed up (or deleted). You can use the parts to recreate what's been damaged — including reproducing the layout of your pages and replacing all your text and images.
If you don't know how to do this, I'd be happy to help. Use the contact form of this site, or call me at 805-643-6993 (California business hours, please).
If you want to rebuild your site elsewhere, check out the Transferring Sites post, in the Categories listing (right-hand column).