Two approach to solve this problem. Firstly, your brain is not used to the movement.
practice tapping your fingers away from the piano.
aim for speed, like semiquavers of (C-E), (D-F) in 100bmp.
when tapping so fast, make sure you don't contort your hand and do unnecesary strains. Movement should be slight, but fast.
Secondly, the muscles in your fingers, especially the 4th, are weak. Try holding D and F with 3-5 fingering, then raise your 4th finger as high as possible, then hit the note E. Repeat until you find it comfortable.