You don't need to run 75 miles per week to run a low 17 min 5k. You could do it off 30 miles although in your case running more may help you regain your fitness. All you need to do is win the race. Then you can say, "I just ran hard enough to win. Wanted to make him think he had a chance."
Run intervals on the treadmill at slightly faster than goal race pace. Get that dialed in. See how long you can last in your intervals. You got this......6 weeks is just enough time to possibly have a chance. Lastly, run smart in the race and just outkick the guy. Don't go out hard like an idiot and blow your whole race.