Well, nobody seem to know a good answer for this and since I need to have it done by tomorrow morning, I decided just to try figuring it out myself. I did watch some YouTube videos but nobody covered the pallet seam issue. I think the main problem is that this pallet board has the edges of the boards beveled. If you flip it over the edges are not beveled and I wouldn't be having this problem. But it's too late now
I pushed the vinyl down as best I could on the beveled seams, then did my basecoat, then topcoat. After it dried I peeled off the vinyl and there was some ugliness in the seams, so I got a toothpick and some gray basecoat paint and touched them up. It doesn't look perfect but it's pretty good still. I'll know not to use pallet boards with beveled seams anymore.
Here's a finished pic;