If you bought it from a reputable online dealer, it isn't a clone. You just happened to get a Tenacious that was poorly sharpened. That's not common on Spydercos, but it does happen occasionally, even on the more expensive ones. They're sharpened by hand, by human beings.
If you bought it some other way, then it's probably not a clone. AFAIK, no Tenacious clones have been reported yet. Granted, that's no guarantee, but it's a pretty good indicator.
Bottom line - purchasing from reputable dealers is the best defense against knock offs.