In my last race a pit took 5 seconds long, i am not sure whether it is the fuel or it is just my pit crew messing up. Is there any way to decrease pitstop times
The pit stop times can't be improved and are minimum 3 seconds for tyres or longer depending on the fuel amount.
Also given your stop time I'd guess 57 litres, give or take, and that's quite a lot and usually in the area where the weight slows the car down way more than the time lost in a pit stop.