Good start and fairly good technicals.
Dog is slightly over-exposed I think.
The DOF is shallow from shooting at 2.8 that his 'face' is OOF
You are shooting at len' worst aperture and a 1/2000.
You could easily shoot at 5.6, where lens is better and DOF greater, and drop the shutter speed.
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The vertical is off and that is easily corrected.
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The stream is off-level (the trees are at a slant) and the water flow is blown out (no detail) in the center)
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Keep on, good for a start.
Yes, definitely watch those "images" that happen to be .09 degree off from perfectly level, since some people are overcome by a simply irresistible compulsion to rotate them so they are "perfectly level".