Hi Jo,
I think it is possible the horizon is too close to center and the two halves a bit too similar. The blue sky gets beach colored at the bottom and the blue sea gets beach colored at the bottom.
I like your style and technique though. My own painting attemps turn disasterous.
If you raise or lower the horizon or like others said put some outcropping in from one side it may give it some tension.
Maybe take some of the horizon sky color into the sea too then it would connect them.
I hope this helps.
pat