Although leg day has the reputation of being the hardest day of the week, it can be a little too easy to cheat yourself. For some reason, people are more comfortable struggling through a heavy bench press than they are struggling through a heavy squat. If you want your legs to grow, then you're going to need weight. It's just that simple.
Complete the sets and reps as I've programmed them. There's no need to add more volume if you've been pushing yourself. Keep your rest periods as short as you can, but don't go into the next set until you feel prepared.