All my printed parts (Cessna 152) have a weight of about 10 % more than the weight given by 3DLabPrint.
Is it due to a too thin layer setting on my PRUSA i3 MK3S, ie should I increase the thickness of the printed layer ?
Increasing the thickness is going to increase the weight. If you are already 10% over weight it will get worse. However…the weights given are a guideline. Different filaments will come out different weights even when printed the same so I wouldn’t worry about it. So long as you balance the plane properly and have enough power it will fly just fine.