Could probably reduce the number of blue colours. Seems good to me, otherwise.

Be careful about that banding on the top of it. You could probably still eliminate some more colours, although that's mainly a stylistic choice.

Here's an edit to show what i mean (and to show how to reduce banding):



My edit is probably not a hundred percent correct, so don't rely on it, hopefully other members with much more experience than me will chip in!

All that aside, it's a good starting piece.