Hey Shayz,
Lovelypurple is right--you really did lose all that weight. And you would have weighed 5 pounds more to start with, had you had the new scale then. So don't fret about it! It's only a number, and it's one you chose yourself.
Revise your goal to 175 for using the new scale. Or, you can decide to keep using the old scale until the wedding, if you really must see that 170.
Jay