First: better than I'll ever be. Nice job. Second: the white at the lower right corner annoyed me at first, but I couldn't figure out why, then I settled into it. Third: I think it struck me as off because this work is a study in perspective focused on the cabin. There's no foreground and the background vanishes to infinity. The cabin, then, suffers from an undue focus and the perspective is imperfect. You did a great job of drawing the eye to the cabin, but the perspective and orthogonality are just off enough to jar. Worthy of note : this perspective study has been presented to us through warped perspective, which is probably magnifying its (minor) faults. The next one, I reckon, will be spectacular.
Thanks! Yeah it took me until I finished to spot the error in perspective on the cabin. I went at it freehand when I should have lined it out with a straight edge beforehand. The background I was attempting to gradually fade from the darker blue to lighter near the bottom (with the intention of painting in clouds on the bottom left, but lack of experience with watercolours soiled that plan!