Problem with wood pulling away

I've just finished my second project with Ana's plans - the king farmhouse bed. I have a question and not sure where to ask. I put the headboard outside today in attempts to let the stain air out before putting it in our bedroom. I think that may have been a mistake! It was in the sun, and when I brought it in today, I saw that the trim piece laying over the panels had started pulling away from the header. Now I can see a gap between the trim and the header and it is showing a sliver of the panels. I know that it had been tightly secured with the screws before. I can't go back and tighten the screws as I countersunk them and covered them with wood filler. I'm so upset as I was so happy with how wonderful it had turned out. What can I do to get the wood to go back to where it was originally? I thought about a clamp and slowly trying to crank it back together, but I don't want to do more damage. Should I add more screws instead? How can I save my project?!?