Installed a new toilet, wrong size, 8 inch gab between the tank & wall

I'm not a plumber, but it sounds like you need to replace it. If you can't exchange it, I would suggest donating it to Habitat for Humanity or other charity that can give you the tax write off.

Hi Teresa! We had the same problem, since the new tank was much slimmer than the old one. I took some scrap wood, the same paint I used on my bathroom cabinets, made an upside down U, and added a small shelf at the bottom to reinforce it (a good place to hide cleaners, etc.). The top, I usually keep a basket for things that I usually keep on the sink. Easy to do, simple building.

Place a shelf over the tank to cover up the space. Make the shelf about 6 inches wide from wall to front. Be sure to leave a little room so that you can lift the tank lid if you need to.