PCB etching troubles. Over etched?
I my experience the etching is not the critical step. It looks like you have problems with light exposure of your traces. In my setup I addressed this problems by using two masks one above the other to make sure they are impermeable to light.

An other possible error cause is the developer. Make sure the powder is evenly distributed before putting in the exposed boards. But as I just mentioned - with a good contrast in exposure this is not very critical.