When you edge glue balsa sheets you need to be aware that with wood glue (even the "water proof" type) the glue joint WILL LOOSEN AND FAIL when you wet the sheet down for bending. It will fail when you attempt to bend the glue joint area.

What I do is edge glue the sheets with wood glue and sand the glue joint smooth. Then, ON THE INSIDE OF THE SHEET (the part that will be inside the plane ) I go over the glue joint with CA (wiping it down/off ). When you wet the sheet, provided you do not flex the glue joint too much, the glue joint will hold together.

If the joint does start to separate, you can use some lite weight filler after it is glued in place to fill the joint and have smooth sanding.