Ok so I tried to apply what you said and took my time on this one

Hi Dennis! I see your demonstrating understanding of the construction for the head in this piece, so good work :) I think the main problem here comes down to proportion. Right now, the face seems to be stretched out vertically in comparison to the Loomis measurements, due to the jaw being longer. It can help to think about the length between the brow guideline and the nose guideline in order to place the jaw, since the loomis model divides these equally. Additionally, the Loomis model provides a rough average proportion for the face, but individual people typically have variations in these measurements, and it's good to keep an eye out for this. In this case, the model has an even shorter/smaller jaw, so it helps to push the jaw measurement even a bit shorter than usual. Another point to watch out for would be values. Right now, they seem a bit unclear, so taking some time to have smoother, cleaner values would help (practicing value scales & gradients is a good supplementary exercise too). The initial lay-in marks and construction lines also muddy up the shading, so working lightly when you start and erasing to clean up as needed can help give more clarity. Hope this helps, you got this!