Hello Nunu_12,
may I ask why do you want to achieve a Y+ of 30?
When having a look at this standard graph on u+ over y+. Please note that one area, the buffer layer, cannot be well captured by the turbulence model. Therefore you usually try to stay away from this region.
So your Y+ values should be in a range from either 0-3, or 30-100.
When having a look at your last image, you are exactly in the buffer layer.
therefore I would recommend you to choose 2-3 Layers and try to achieve a mesh in the range of 30-100.
Best regards
Sebastian