I have genuine Cokin P filters and holders. They are tight but not THAT tight. It takes my holding holder firmly and push with few fingers. Unless I have it going in very straight, filters get bound up and won't go in.
My filter holder has "Cokin" embossed at the very top where the lip defines where the filters should reach. (does that make sense?) On back of it, it has "Made in France" and "Patent Pending" at corners.
Cokin brackets are pretty inexpensive. You might just want to get one if yours isn't genuine. If anything, I'd file the bracket, rather than the filter itself.