May be a bit of communications difference? Bow means and arch or dip in the length of the wood. But you show a bit of gap that I would call twist? Not meaning to pick nits but the two would give me different thoughts on how serious it might be. For a bow where the tank will not set down firmly at all points along the edge, I might want to redo to get it all level. But for the gap and what I would have called a twist in the front board, I would not bother too much.
A couple thoughts? Is it possible that the gap might be due to the end of the short board not being cut totally square? Easy thing to happen that would make a small gap that would be no trouble, ever.
A second thought if it really bothers you enough to fight it, is to get a large clamp like a bar or pipe clamp to put across the top and pull the front board into line. This would require any top to be refastened and I might not bother but your choice. Not a major structural problem that I see unless the wood is green enough to continue twisting as it dries.
For me, I would simply watch and not worry until it really did something more.
The 2X lumber is not a perfect world when building and a 250 is one way to hold things down so they don't move!