Hmm I don't agree. That spacing looks right to me, but, now you mention it, the E,F,B and C notes look quite a bit too wide, I think that's the problem.
The spacing of the black keys is so far from the actual spacing on a real keyboard that I question how it could possibly look right to you. I would love to know if you actually have a real physical keyboard on hand, like I do, or if you are just going based on memory.
You should check out google images for piano key clip art. Almost all of them get it wrong. They assume a black key is centered between two white keys, but that is only true for g#.
The width of all keys, white or black, should be equal to one another at the back of the keyboard.
The width of the white keys should be exactly equal to one another at the front of the keyboard.
Those can't both be true (since 5/12 isn't equal to 3/7), so the former has to be fudged a bit.
Literally just came across this thread after playing piano for the last couple hours, and I wouldn't have noticed it if it weren't pointed out. I think when you play you're just used to seeing all kinds of shorthand. I remember portable synthesizers from the 80s that actually did have this kind of relative size on black keys.
The spacing of the white keys is correct in the sense that they are of equal width. However, the black keys on a real keyboard are not centered between adjacent white keys (except for the G# between G and A).
The placement so that the two groups of black keys, C#-D# and F#-G#-A#, are a little bit wider than the naive on-center placement, as if they were repelled from each other.
The thin parts of the white keys that are between the black keys are evenly spaced with the black keys: i.e. all 12 semitones are equally spaced at the back. The rear ends of the keys directly link to the striking mechanism, which lines up with evenly-spaced string courses.
