The trick is to follow the reference closely, even where it's different from what your brain expects. The reference skull has a flat spot in the middle of the forehead, between and above the eyes. Your brain is telling you the top of the skull must be a dome, and it misses the flat spot altogether, which makes it look wrong.
Here's my take, I didn't attempt a wood grain:

You palette has some lights and darks, with several colors very close to each other on each end and not much in the middle. You might want a better set of midtones. Oh, and I goofed up the teeth some.
Tourist