Hi Daniel, If you want to put in a hill session, I'd advise doing this on the Friday rather than the day before your rugby match.
The extra 3 mile run is optional - I doubt it would take anything away from your rugby performance the following day, but it's perhaps the first thing to drop if you're feeling tired.
If your aim is to be good at rugby, I'd advise finding a short, sharp hill - perhaps of about 50 meters and, after warming up, run 10 - 15 reps hard with walk back recoveries.
If you're also looking to improve running, try the occasional 2 x 20 minute loop over a longer but shallower hill - perhaps of about 800m. Rather than reps, run continuously up and down the hill. This is more of a 'threshold' workout and will give a big boost to heart & lungs as well as leg strength.
Or alternatively combine them - maybe 2 x 10 mins on a shallow hill, then 5 - 8 reps up a 'sprint' hill.