I have some woodworking experience making bookshelves and tables. But apparently not enough...

I built a fireplace surround with mdf for the bulk of it and some pine and pvc moulding. But for the mantel itself I used 2 pieces of 7ft long 1x10 pine, screwed one top of the other to make it thicker. It's the better stuff with squared edges and no knots or sap.

The whole thing looked great until I primed it. Then I noticed that you could see the gap between the two pieces of pine used to make the mantel. I didn't want to take the whole thing apart at this point so I tried wood filler on the edges. It looked good, no crack. Then I primed again and waited a couple days. The crack is back.

I used screws (I think 3") and went all the way through both pieces and into the surround legs and center. I did not use glue. So any advice on what I can do at this point? Unscrew it all, use glue between them and screw them back together? Use edge banding? (although I looked into this and it would be expensive because the usual 3/4" wide tape won't be big enough) Separate the two pieces and chunk the top piece altogether? I'm not feeling brave enough to try trial and error again. Thank you.

Amanda