Can you tie conductors together on lugs?
Definitely not allowed!
If you want to do that, then shop for certain spec-grade switches and receptacles ($3 instead of 60 cents), which have a feature some call &quot;Screw-and-clamp&quot;.  This allows you to back-wire 2 wires under each screw, and you tighten the screw to clamp the wires.
Also note that since it's in a metal box, your switch does not require a ground wire.  It will pick up ground via the screw threads and head.   This trick doesn't work for receptacles unless the receptacles are labeled &quot;self-grounding&quot;, which most of the &quot;spec  grade&quot; receptacles will be.