WAIT! It's possible you MIGHT have to adjust the stand-offs, but maybe not. They MAY be pre-installed just right for your mobo, or may not be. So, with the mobo NOT installed in the case, inspect carefully and compare.
Here's what to look for. Every mobo has several mounting holes. You put a screw through each of those into the threaded holes of a stand-off under it. The mobo is supposed to be grounded to the case at those mounting holes ONLY, and no-where else. Note around each such hole there are tiny metal "fingers' to contact the screw.
Ideally for mechanical support you want a stand-off under each mobo mounting hole. But what's REALLY important is: there must NEVER be a stand-off under the mobo where there is NO mounting hole. A...