Welcome Dominik.
Great wood and nice pens. You are doing great for first pens and I know that you are excited. These are better than my first few!
You did ask and I will pass on my observations - there are two things that may improve the pens:
It appears that I can see either turning (chisel) marks or course sand paper marks. I would guess chisel. That would suggest chisel needs sharpening. If it was sandpaper, finer sandpaper will take the marks out. Also, sand parallel to the lathe - or longways when the lathe is stopped.
If it is the chisel, very few people come into pen making with the ability to properly sharpen a chisel for turning pens. That usually comes later after they have turned several.
Another thing about the marks is that sometimes that is from the type of chisel used for the type of wood. If you don't have carbide inserts on a chisel then you will have to sharpen the chisel.
On softer grain woods - a skew does much better;
On harder woods, a skew will work good but a scraper will work better on very hard woods in general.
Hope this helps. Lots of great helpful people here with lots of experience!