Ruined birthday present surprise.

So my birthday is tomorrow. I went into my sister's bedroom to get a top she stole from me and I had to go into her wardrobe to get it. When I went in, I saw a PlayStation 4 - something I've been saving up for, for ages. I gasped and made sure that she couldn't tell I had been in there. I'm so happy and I genuinely feel bad because I know she probably spent a lot of money on it.

But, I am so excited right now. I feel like I've ruined the surprise so does anyone know how I can pretend, when she does give it to me, that I knew nothing of it? And how to I disguise my excitement right now until tomorrow? I need to take my mind off of it otherwise she'll know that I know about it. Thanks :) x