What's wrong with my timing diagram?
Some pointers on timing diagram in general


Removing the horizontal axis lines helps with understanding the waveform better
Mark a vertical dashed line on clock rising edge (not needed on every clock edge but on important events).
Make sure to show the data (D) meets both the setup and hold window of the clock by pushing it a little bit after the clock active edge
In order to make it even more realistic you can always add the slew of the signal by a sloping transition as mentioned by @Neil_UK in the comments section