The bad manners aren't yours - they belong to whoever told you that you are wrong for holding the knife and fork the way you do. Now THAT is rude! As long as you don't shoot food across the table when you cut it, or drop morsels in your lap when raising your fork, I see no problem using a knife with your left hand and fork in your right. If doubt if anyone at these important business dinners you have coming up will even notice - or be ill mannered enough to comment.