I think the problem is actually the enormous high current switching loop you have routed through your board. It is so large it does not fit in your picture, but here is the part of it I can see:
Depending on how far it goes to the right of the board before meeting back up and closing the loop it is actually a little surprising the converter works at all.
Here is a better layout for that converter:
By putting the diode and MLCC capacitor right up against the switch, current only flows a few millimeters and all on one layer, so it encounters only a small amount of resistance and inductance which leads to lower losses and better performance. Furthermore that distance is mostly connected with wide planes that have lower resistance/inductance. Note that depending on the switching frequency you may also want to put that big electrolytic capacitor in too, but you can parallel the MLCC to keep the loop area small and put the electrolytic slightly further out.
When I built that converter like this the chip did not get particularly hot.
Edit: If you wanted to try and salvage the existing board, you could try adding an MLCC and a (short!) jumper wire here:
That would reduce the loop to the green area. You could test that and see if the temperature is reduced.