Considering the questionable origins of many tartans, who really cares? Don't be overly concerned with the "short-bread tin mentality" that some apply to highland dress - chances are you're already taking it more seriously than most Scots. Just don't wear spats or swords or wrestling boots and you'll be fine.

If for some reason someone gives you trouble regarding your "right" to wear a particular tartan, ignore them. You didn't want to hang out with them in the first place, as they are crazy.