Empty Inside?

So I'm just finishing my second batch of Christmas cards. On Tuesday, I took 39 of them to the post office. This morning I finished making the last 11 of them and am just about to take them to the post office. That's 50... right? Well, somehow, I managed to have one left over to keep for us. So that means that I made 51. But I only had one pack of 25 sheets of red cardstock when I started. Times two cards per sheet equals 50 cards. And I never opened the second pack that I purchased. So how in the world did I end up with 51 cards??? It's not even possible. I checked to see if maybe somehow I actually had 26 sheets of red paper to begin with but that would mean that I would have the other half still left over. No left over other half to be found. So then I recounted all of the checkmarks on my list. 50. And still one left for us. WHAT DID I DO?? I can't figure it out. The only thing I can come up with is that I accidentally sent an empty envelope. Even just the thought of this embarrasses me. I can't imagine how I could have possibly done that, especially because I tried to sign each one specific to who it was being sent, but, I don't know! It's quite the conundrum. So, sigh, if you happen to receive an empty envelope from us, please let me know and I'll send you a card and I'll try not to cry from embarrassment. Off to the post office I go.