That looks like my first attempt at dovetails. There are numerous good videos out there and the techniques for good joinery, and dovetails in particular. You will get there if you are willing to study and practice. If I understand the question, you want to know if the issue with the gap at the tail and pin baselines are the result of mis-measurement or chisel technique. My guess is that it is probably some of both along with other issues. Even with perfect “measurement”, however, imperfect technique will result in an imperfect joint. I have seen masters of the craft make world class dovetails without any “measurement” save matching one board to another and their well-trained eyes, practiced hands and time proven techniques. Dovetails were considered an everyday, basic joint by cabinetmakers of old and the only advantage they had over you and me was the techniques perfected over hundreds of years handed down directly from one craftsman to another, and the benefit of doing them day-in-day-out.
There is nothing about fine joinery that cannot be mastered through study and practice. It would pay to round up some scraps and do one set a day for the next couple of weeks.