Im new to this, and I just can't figure out how to mirror this shape

Ive been at this a few days now, this is my 2nd part.  It is a faceplate for a radio I have been working on.

As you can see, I sketched out the pattern on one side, and made it a hole in the plate.  I like this cutout, now I just want the same thing on the other side of the plate, mirrored. 

I am pulling my hair out trying to figure out how to do this.  I think my features are a little messy too, I don't even know how to merge features into one feature... I would think I need to merge the separate sketches first before I can mirror them to the other side.   I just don't know. 

I traced out the skull pattern from an image, so I am proud of myself for that at least!  Please help

https://cad.onshape.com/documents/f9d429bd124c8f68e9968c91/w/a54be6d14289a32852da0a64/e/d77ad3f3d1bc61bc7c0a09c1

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