1. Congrats on getting out there and doing it.

2. Sprinting is not really what you need to be focusing on now. You need to develop your overall fitness, so you can hang in till the end where sprinting becomes relevent. Doing sprint workouts is fine, but I think you'd benefit a whole lot more making 2 x 20's your core focus.

3. You do need more miles. Doesn't have to be a ton. 10 hours of week, of well planned, focus time will be enough.