The only drawback is that by the time you get to your size goal (or at a size that is dramatically bigger than she could ever remember), it will most likely be years later (let's be real here).... by then she'll be married with kids. And by then, after all that time, who would even care? Would you still care? Penis growth takes a loooong time, man.
The whole stunt could backfire so easy, it's not even funny. You could whip it out to NO reaction... after all that time and work, you pull out your pride and joy thinking you'll shock her, and she won't even notice. No matter how big you've gotten, she could still diss you and it'll still hurt.