A good day trade SDS

SDS is the double inverse of the SP500. This past Friday I entered the day without any ideas, was not really looking to trade. I noted bullish sentiment from others. The market opened up about half a percent for the SP 500, I think it was up 6 points or so. I figured that on options expiry with so many people bullish we just could not continue with a strong morning rally. I entered SDS I think within the first 15 minutes with a mental stop of its low of the day, my target was for it to get back to where the market closed the day before. I thought about just putting in a limit sell order and going about my day. Instead I went about my day with frequent checking of the action. When I saw that my target had been reached I put in to take my profit. My gain was almost twice what I risked.