It may of just had some dirt or something on the threads which made it harder. You would almost certainly know if you cross threaded it. If everything is working fine I wouldn't worry to much. If it aint broke, don't fix it
If you really think you may have cross threaded it, take it out. Inspect the threads of abnormal wear. If the threads look ok, then put it back in, if the threads are all messed up, get a new plug and make sure the thread on the engine are looking decent. Put some antiseize on the threads if its not already on there.