Here's a trick to keeping the good side of panels flat when edge gluing.
Board w/blue clamps and sander

Purchased lumber can vary enough in thickness to show "steps" on an edge-glued panel. Fortunately, most panels need only one "good" face. To keep at least one surface flat, edge-glue panel pieces with the appearance side down and pressed firmly against the clamp bars or pipes as you apply clamping pressure.

1 Cover the clamp bars or pipes with painter's tape where the pieces will rest. That prevents the metal from discoloring the wood and simplifies removing glue squeeze-out.

2 Press the pieces down onto the clamps as you tighten them. Leave the glue-up clamped for an hour, then remove the clamps while the squeeze-out remains soft enough to scrape off. Allow the glue-up to dry overnight.

3 Working only on the appearance side, use a random-orbit sander with 80- or 100-grit abrasive to level the joint lines, as shown. Avoid creating a trough in the surface above each joint by continually moving the sander and smoothing the entire panel evenly.