Twist is easy to detect on a flat bottomed wing (rubber-band dowels near each wing tip and stand bach a few yards and look to see if the dowels are even). Sometimes it takes longer to find two straight dowels (I have arrows that makes it a bit easier). It's a tad harder on a symmetrical airfoil, but you can do it with equal sized blocks between the wing and the dowel near the trailing edge

An incedence meter makes it fairly easy. If you can't measure it you shouldn't try to correct it. If correcting the uneven ailerons helps, and you'll have to fly it to test that I'm afraid, then you should probably either seek help in person or invest in an incedence meter.

Some folks are good enough to spot it visually by setting the plane on a level surface and sighting along the wing from the rear, using the horizontal stab as a point of reference.

PS - when you do fly it again resist the urge to yank it into the air to gain altitude. Get up plenty enough ground speed and then fly it up at 15º of climb. If you yank it and stall it even an untwisty wing with even ailerons won't save you.