Just tell the truth, it's a pretty petty thing to lie about.
A woman will pick a truthful guy 9 times out of 10, and that 1 isn't worth the hassle.
Plus women have an innate sense for liars =P
Trust me mate, just go with the truth. If she gives you a hard time over it take it with good faith, a joke between friends is no big thing. Plus if she cares about you she won't care anyway.
Like DeLux said, she might have her own silly story about doing something along these lines to share.
Either way mate, best of luck on your date and the many more to come ^_^