Out of square walls and prefab countertop

I'm installing a prefab formica counter top with an integral backsplash and bullnose front. The mitered tops assembled square, but I'm stuck with a problem. The scribing strip is only 3/8", and my walls are about 5/8" out of square over the length.
The right countertop is 70" and will have the end visible from the room. The left is 54" and the edge will be next to a fridge.
So, what I'm thinking of doing is to use the scribing strip to get the right top flush to the wall. I think since the out-of-squareness will swing the shorter countertop out less, and since the shorter top will have its edge hidden, any errors should be on the shorter side.
Since I don't think I have enough scribe area to fix this problem, I'm thinking of putting a corner round on top of the backsplash to hide the inaccuracy.
Comments or advice?
Lastly, I don't own a belt sander. What other ways could I go about removing material from the scribe area? I do have decent tool collection, just no belt sander.
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I would rework the miter using coarse sand paper on a wood block - no, I would use my belt sander and finish with the wood block. You don't need much change in the miter to get closer to the walls.
Use the scribe strip for minor in and out variations in the wall surface. A jig saw and a coarse sanding belt wrapped on a board or dowel makes a slow substitute for a belt sander. No one to borrow from?
1/4 round or wide caulk joints can make the job look a bit amateurish.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing. . . . DanG

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Yeah, I'd read a couple older posts that recommended not doing that, since it's hard to get the miter correct, so I went and glued up the sides last night, figuring it'd at least give me a more stable reference. So, redoing the miter isn't an option, unless I buy two more tops and use these for a very long, backsplashed router table. :)

Yeah, I got that to deal with, too. The longer wall humps out about 1/4". The shorter one about 1/16" near a stud.

Eh, I just went out and bought one. It's the wife's project, so she's not protesting when I score tools for it.

I hear ya. I'll avoid briding the gap with caulk, and I'll get things as close as I can adjusting the scoring strip, but I think I'm going to have to use something as a cover here. I might go with a nicer trim than quarter round. I've got some I'm putting around the kickplate. Those'll be black. I might use the same trim, in white, around the backsplash, since we have a pretty prevalent black-n-white theme. If it ends up looking amateurish then, well, at least everyone will know I did it myself. ;)
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Thanks for the help! It turned out ok, without the need for trim. I was able to jigsaw/beltsand well enough to get it within acceptable caulk-tolerance. What I didn't account for in my original post is that I had two 3/8" strips to work with, and 5/8" of error to account for. 3/8 + 3/8 = 6/8. I just took my time, was careful, and went through more test-fits that I'd bargained for. I did take nearly all the scribe area off in one part, but that's in the far corner and does not look bad at all. I'm sure I'll stare at it for the next 20 years and think "Damn" but I'll be the only one.
Thanks, again!
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wrote:

Cheapskate. I went for the $44 model. :) It's not my best tool, but got the job done (which makes it the best tool I've used today!)
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Don't use quarter round, that would look just way too trailer park.]'
And if you don't have a belt sander, use rasps and files.

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As a last resort you can always cut out some of the drywall and push a little of the counter top into the wall.
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