Legs not quite right

I'm starting back with this running thing. Turns out, I'm in worse shape than I thought. Two months off has made for quite the drop in fitness. My five mile effort tonight, at what should have been a ridiculously easy pace, was more of a challenge than I'd like to admit. I'm happy that my form stayed good the whole way, and my cadence was a crisp 90-92 spm for the entire run, but when my heart rate was 161 bpm at the end, instead of the ~150 it should be, I know there's a lot of work to do. I guess I should be less anxious but starting to race again, since right now I would be bringing the proverbial knife to a gunfight.

Run: 5 miles @ 7.5 mph