I've used malted wheat instead of torrified wheat by mistake in making an ale
How ill this effect the final product?
Torrefied wheat can sometimes be drier, and create a good head without haziness in the beer. But if you are only using a few hundred grams / 4-8oz and not brewed the recipe before then relax, your beer will still be fine. If you have brewed it before, you might find the beer doesn't taste as crisp/dry as before.