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No, you shouldn't check mirror. Gerber plots are meant to be read from the top down - just like your PCB editor shows the board. The Mirror ability is there for those who want to etch their own boards, or the odd fab who uses very, very, old equipment.
If you press the button at the bottom of the display for "Plot Layers", you'll see a choice for "Used Layers" - click on that and the appropriate layers will be checked for you.
Depending on what you want for your finished board, you may not use all the Gerber layers. For example, if you choose not to have a top silkscreen, you just ignore that Gerber plot.