Laterally balancing while building is important. But don't forget to complete the job with flight testing.

Trim for straight and level flight, then roll the plane inverted. If the roll is still trimmed correctly, you've got it balanced. But usually it will roll a little one way or the other. If the plane rolls left, then the right wing is a little heavier. Add weight to the left wing tip and try again. I use small chips of stick on lead under the wing tip.

Dave