I assume that with two coats of Future that the surface was very smooth. That's the first mistake many people make, they try to do a wash on a flat surface. When a wash gets down in the matte of a flat surface there is no way I know of to get it out.
What kind of paint did you use for the wash? I use either artist's acrylics or artist's water colors. My preference is water color because it does come off much easier. Even though many people have very good luck with oil-based artist paints or enamels for a wash, that's way too risky for me. The water colors and acrylics work fine, so that's what I stick with.
If you used an acrylic paint for your wash, this is what I do when it is stubborn and won't come off.. Dampen a Q-Tip (cotton bud) with mineral spirits. And when I say "Dampen" I mean just the slightest hint of moisture, you do NOT want it very wet! I dampen it and then push it against a paper towel to get most of the thinner out. Then LIGHTLY rub your excess wash with that. Be careful though! It will go through the Future and paint if you rub too much or too hard.
Also, when rubbing the excess off, rub across the panel lines, not along them. This leaves the paint in the recess but gets it off of the surface.