First medium distance ride

Got my bike little less than a week ago and have been doing 8 mile rides. They seemed pretty easy so I figured why not double it… well this was a lot more difficult. By the end I was struggling pretty good. My main form of cardio before this was running but due to a meniscus tear I had a lot of time off and figured biking was the best options. Well I’m absolutely loving it so far, I’m not that great right now but I hope to bounce back soon!