Judging from your username, I'm guessing that you're just starting M-2. During M-2, you will have LOTS more time to get familiar with physiology, as normal physiology is generally reviewed when each system is discussed in pathophysiology.
My suggestion would be that as you cover each system during M-2, read the corresponding chapter in BRS Physiology, and do any highlighting or underlining that would help you. Then, when USMLE studying comes around, you've already read the book once and can read it again.
Don't try to read any book during your last few weeks before Step 1 that you think would take longer than 3-4 days. You probably will regret trying to read STAR in 3 days. Better to get super-familiar with BRS during the year -- makes it much less painful later on.