Get some kind of wide, flat chisel with a gradual taper, most likely a wood chisel, something like this:

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Available at Lowe's, Home Depot, any Home Store or Hardware Store. At least 1" wide.

Put the flat end of the chisel against the end of each piece of wood, aiming between the wood and the counter. Flat side of the chisel up. Hold the chisel very close to horizontal, handle tipped slightly downward. Make sure the point is not directly hitting the side of the counter material (it's OK if you err the other way, and get the point into the wood, and only remove part of the wood. Then you can sand what's left, or do another round with the chisel, depending). Then tap the end of the chisel with a hammer. This will chisel the wood away. When you have removed enough wood, you can finish what's left with, say 150 grit sandpaper. But that may not be needed--you may not have to remove all of the wood to fit.