Nope...don't think it's a letter opener...
Some gunongs are, indeed a little on the small side, those yours does seem pretty small. Perhaps it was made for a woman or a child. Do the fittings seem to be silver? Is the pommel ivory? It almost looks a bit like clam shell, which would probably be rarer than ivory, but i can't tell from the photos.
Your blade looks like it isn't laminated, but i would give it a light etch with vinegar to be sure.
Bottom line, i would say that you did not screw up, unless you paid a great deal of money for this.
