cube missing parts?

[Leuxll]

Hello, my cube is missing a triangle. Does anyone happen to know why this might be happening? Also, the lighting seems a bit off, does that matter?

[Zhecheng-Wang]

You can see there are edges crossing another edge (see the "x" shadow lines on the yellow face).

Your F is wrong so you are connecting the wrong vertices, think about how you should connect the vertices for one cube side.

[Leuxll]

ahhh yes, i got it now. Thank you very much!