Please explain to me this

So I have started this couch to 5K. I am wanting to be toned for this summer. So I check my sugar before I start I like to be around 150. I think I wont go low and I will end probably in the 90-100 range... WRONG!! Of course it doesn't do what I think its gonna do. Guess what I am not even close and no I am not low. I was freaking 303 when I got out of the shower after my run!! I checked ketones none there but seriously!! SERIOUSLY! 303! Did my body go into shock? Can anyone explain to me why my BG went up instead of the normal going down? Isn't that what is supposed to happen? I always thought when you exercised your blood sugar starts to drop or have I been completely wrong about that this whole time? BTW this has not just happened once its happening every time I run... Maybe I need to find a new exercise...