Custom fixed gear, road geometry

Did you build the frame? Interesting modified head tube lugs.

It seems the upper cups of the headset don't seat properly. theres a gap of 1,1mm, should I be worried about this? when i took the fork out, the cups would only seat properly without the black seal, is it supposed to pop/snap? I didn't want to overtighten the bearings. (yes I have the bigger bearing balls in the lower cup). For now it does not seem to be a problem, it runs really smooth.

Are you talking about the threaded upper headset race that sits on top of the bearing? Is the fork steerer slightly too long? Threaded headsets need the steerer to be pretty much exactly the right length. You could try it with a spacer between the race and the locknut and see if it seats properly then.