Welcome, Marek. Two things you need to do differently:
1) Files go in D:/games/Company of Heroes Opposing Fronts/WW2/data/scenarios/
mp2) In order to see .sgb maps in skirmish mode, you need to start CoH in "Dev" mode. To do this, make a new shortcut to the CoH exe file. Then edit the shortcut properties and add "-dev" (no quotes) to the end of the target line. So the line should read:
"D:/games/Company of Heroes Opposing Fronts/relicCOH.exe" -dev
(or whatever the .exe is, I can't remember it off the top of my head)
Then, run that shortcut and you should be able to see your map in skirmish mode.
If you do not, please provide further updates. Good lucK!