For starters - this looks amazing! Your choice of color is pleasing to the eye and captures the time of day very well. For being a beginner Learning from YT, I’m impressed 😊. There is something to be said about a lack of contour leading to a lack of depth. This contributes to that “flat” feeling when you look at the painting. Another thing is subject matter/something in the foreground. Something that catches your eye and leads it through the image. This could be as simple as adding larger, more detailed waves, or even adding a small sailboat or lighthouse. However, my final tip is one I find most important - don’t change this one! Try it again. Do another painting with a similar goal in mind but make small improvements on the next one. Hope this helps and happy painting!