cmos battery alone is not enough to short anything.
Make sure you plug the plastic standoffs that came with the case/motherboard. They support the weight of the motherboard and also other components you attach to it. So try spread them out evenly for best support.
You should have insulated washes for the screws as well, red looking washers. Dont necessary need to use them as long as the screws aren't too tight. Better to use them anyway since they should be in your possession.
There are numerous tutorials on how to build your own computers, just make sure the motherboard is in noway contacting metal from underneath.