When there is no suitable boat, branch, twig, whatever there to be an interesting foreground, then moving the horizon can help composition not to be quite as boring, the rule of thirds applied maybe even to extremes could help, creating a very low horizon and lots of sky if the sky and its vastness and magnificence is supposed to be the theme of the photo (clouds in the sky would be nice for that concept!), or much more water could be included if the vastness of the sea is the main subject (but in that case - here I thoroughly agree with Alex - a boat would also help - like the clouds would with the sky).
Whenever you take photos of a water surface, make sure you get the horizon absolutely straight, else it looks like your frame will have to leak and the water will run out at one side.
I see you are still very young, only just turned 14, so you still have ever so much time to learn and learn more - that's what we're here for.
Welcome to ThePhotoForum, Emma.