I'm doing something wrong

Last night I attempted to run a mile, but after 9.5 min and .8 of a mile, I was completely breathless. Sadly, I made myself stop. I did run a mile this morning, in 10:41, but again I was breathless. I don't think my cardio is great right now and I'm not sure why. Should I be riding the bike as well as running? I know I'm doing something wrong, but I'm really not sure what it is...