Concerned with my run workouts

I need to start adding some distance to my run workouts to get ready for this 1/2 marathon in September. I think that adding 1 mile per week to my long run should do it. I don't have to get to 13.1 miles before the race but I would feel good to get a couple 11 miles under my belt. Ran 6.5 miles today. 93 degrees and my legs could still feel the effects of the track workout and yesterday's power intervals.

Distance: 6.5 miles Pace: 9:03 Average HR: 163