Rewarding mistake

I felt disappointment with myself today because of yesterday's trading. I was watching the market, had a really nice call that gbp/usd will fall back from 10:10 high of 640 back to the 600. I didn't trade it but I was paper trading it in my head, just watching. I was more happy that it went that way than sad because I didn't enter. It was sell of into the news of 10:30 after really bad morning for gbp/usd. Sell off really got extended fast to the 550 area. News came and there were no big reaction and as soon as spread came down on Oanda from 20 (news spread for gbp/usd) I entered because I thought now there will be short covering because of no reaction more down. So I entered with half size and exit when it had first bump. Than when I was looking at my p&l something didn't add up. I entered full size trade and not half and I wasn't aware of that. So omission doubled my profit to +17 pips.