I'd match the Front Derailleur to the Rear, but that's just an aesthetic thing...functionally you can use just about anything.
Rear Derailleur - You are adjusting the wrong screw. The small gear is "H" or High gear. The Big one is Low, or "L". Back the "L" stop screw out a bit and you should be able to get the Big Cog. I get the two confused frequently and remember it by Low = Slow, High=Spry
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--Don't Panic.