Dimensions and thicknesses
Regardless of the dimension that you are modeling in GeoGebra, your model will be rescaled and exported to STL automatically with ~4 cm on its bigger dimension. For instance, if your model in GeoGebra looks like 6 x 6 x 8, then it will be exported to STL as 3 cm x 3cm x 4cm.
If you want something bigger or smaller than that, you can still rescale it in the 3D printer software.
The thickness of all objects in that case will be rescaled as well. By default, GeoGebra is exporting to STL under the follow dimensions:
ø 3.5 mm for curves and segments;
ø 3.8 mm for points;
~ 3.2 mm for surfaces.
You can find more details about that in Setting the 3D printer software.