You can't

Remove it, the mistake is obvious

Sell it and make another one.

Different mantle the correct size. Measure 3 times and have a 2nd person double-check your measurements.

If you absolutely have to keep it, could you turn it upside down? Yes, the top would be narrower but it wouldn’t stand out as much from a distance.

Take the mantel down and don't replace it. You have a nice-sized bold piece of art work that can stand on its own without a mantel below it. Put your family photos elsewhere. Fill the firebox with white birch logs and call it done!

thanks everyone for your suggestions! problem is, I don't know how to get it off the wall since I had a handyman put it up!

This is a no brainer. If you can’t take it off yourself, have the handyman come back to remove it. There is no way this will ever look good undersized.

Sometimes, you just have to swallow mistakes and chalk them up to a learning experience.

Unfortunately, your handyman did you no favors. If they could see it was not working, it should have not have been installed. Bad handyman. Find a new one. I would recommend starting over. But with a plan in mind.

1. Don't buy a mantle until you've given thought to what your underlying surround will be.

This could determine a new width and depth, so why pay for it twice? And BTW, it doesn't have to be ALL tile like it is. Browse fireplace surrounds on HOUZZ and you wlll see what I mean.

They are not all tile. Not knowing what your home's style is, its hard to comment on which to do. I know you can never go wrong with wood. It is natural and blends with many home styles.

see photo. Most come unfinished - simplest models are around $300 and can either be stained or painted. If not wanting to finish it yourself, take it to a cabinet shop and they can do it for you.

2. Paint the tile to get rid of the stark white builder basic 4 x 4 tiles. Rustoleum makes a product just for tile. Its a two step process, but performs very well. It will diminish the grout color too.

Then if so choose, you could leave them a solid color or stencil them to create a totally different look.

Even putting a piece of cove moulding on the end of the tiles would help them look "finished".

3. If you are on limited funds and in the fix it now mode: Buy a prefinished "floating" reclaimed shelf (usually 48-60 inch lengths) . See photo.

Then if and when you do redo the entire area, the holes in the wall from the mount screws can be filled in.Just be sure to let the wood shelf be 2-6 inches past the tiles for good scale. Now the math: These are just examples -plug in your actual dimensions for your particular application.

tile width (L >R across entire width) 48 inches

extention of shelf past tile 3 in. x 2 6 inches

_____________________________________________

total shelf width to order: 54 inches ( or closest dimension)

In this example, since 54 is closest to the available 60 inches , order the 60 inch. It will

work.Just center it above the tile and mount according to included instructions.

Good luck and hope this helps.

First thing that comes to mind if you want to hide it instead of fixing it at this time.....I would put a plant on the mantel...one that vines and hangs down. If both sides look the same in shortness, then put another plant on the other side also.

Take the mistake down.

I would go with any of the suggestions that say replace it or leave it off completely. That’s definitely best. However, if, in reality, that will take a while or more money than you want to spend just now, how about drawing a line from floor to ceiling on either side (don’t go as far to the left as the light switch), then paint the area white to match the tiles and minimize the mantel length. You may fool the eye just enough to live with it. Rehang your art, no Command strips or family pictures. After you’ve eventually redone the fireplace, repaint the wall back to the way it is now.

I like Nancy's idea of painting the mantel white and drawing a line between the tile and mantel and painting it white as well. That will help disguise the size difference.

sorry, but it's just wrong. painting it or turning it around isn't going to matter. Any way you can return it? honestly, there is no way to make this work. it's just too short.

(houzz won't let me post photos, or some photos. they just disappear)

you have a simple tile fireplace so just do a simple mantel. you can get a 2X6 beam at home depot, have them cut it for you and stain it yourself for less than $40. Call out a diff handyman (because this one should have told you that this one was incorrect) and install it. or, look how to install it yourself. it's not that difficult.

something like these are all you need

Your piece should fit like this one that's under the wood portion. see how far out it comes? (the white mantel)

or, paint it white. you could also get side piece for it and bring it all the way down to the hearth (but if you're replacing the tiles, I wouldn't bother w/this. just do the single piece)

You must replace the mantel. Measure twice. Cut once. Think three times before measuring or cutting. You are lucky it’s a relatively cheap error. Maybe you can sell the other one or use it for a book shelf somewhere.
Construction 101!

New mantel- longer & deeper. You can use painters tape to play with new dimensions that look suitable. Mistakes happen :)

That shape wasn't really correct for your room. Ready made mantels on Amazon. Don't select one with brackets.

https://www.amazon.com/Best-Sellers-Home-Kitchen-Fireplace-Mantel-Shelves/zgbs/home-garden/16188188011/ref=zg_bs_nav_hg_5_16188187011

https://www.amazon.com/Pearl-Mantels-496-60-Lexington-Unfinished/dp/B005EI5U0S/ref=zg_bs_16188187011_24?_encoding=UTF8&psc=1&refRID=DPW9CRB6DPB0ZSWGA7Z5