Help, is this creepy?

I have written a letter for my girlfriend (it's tied together nicely with a red ribbon in an envelope) and I want to give it to her overnight, as in, deliver it to her house. But I'm not sure how I should do this. If I put it in her letterbox, her parents are going to ask a lot of questions and I don't want to put her through that. If I climb her fence and tape it to her window, I'm afraid that is too creepy and weird. I want to be as romantic as possible, without actually handing it to her. Thanks in advance for any help.