Hi @cecca98!
I am not satisfied how the geometry looks like. You already imported it with a background box which is kind of odd and I would not do it that way. Upload the model as a standalone model and make sure to group faces inside SolidWorks if that is even possible. You can also create separate STL files and merge them which is demonstrated in this workshop here: Merge STL - FSAE Workshop.
This is the approach I would choose. Maybe @vgon_alves or @Get_Barried have another tip for you.
Best,
Jousef