I've always heard that that is too wide for edge joining 3/4" lumber. I can't remember the time honored width but it's between 2 and 2 1/2". One way to help insure the panel stays flat if you are going to use boards that wide is to cut kerfs on the bottom side of the panel. I would go about 1/3 of thickness deep and about every 1 to 1 1/4" apart. This helps release any tension that can build up from the humidity changes. I did that on the mantle top over my fireplace and it's never moved that I could tell over about 20 years. I burn wood 24/7 from October to April pretty much and then nothing from May through September so it sees some major humidity changes.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.