If they added a shift (from a swap or offering you more hours for whatever reason) it shows up online but if they don't print a new copy, it won't be on the paper one, so I assume the online version is correct. Either way, if you didn't knowingly take additional hours, I'd ask someone about the discrepancy.
My HR team has always said to go by what's on the printed grid if there's a discrepancy between My Time and what's posted. My Time has a tendency to do random things that aren't even in the system (I've had so many split shifts shown that I wasn't actually scheduled for it's ridiculous). I don't even go by the target.com/viewschedule anymore. I use wss.target.com/selfservice - it's always identical to the printed grid as well as My Time through eHR. I would still double check with your HR team thought.
I always go off the online schedule. If you don't feel like working those days though, you could just not show up then show them the paper schedule if anyone says anything.
If you're talking about the schedule that you can access from home, that one is usually wrong. As of right now, it's showing different shifts for me than the mytime schedule shows at work.
Like for instance, the mobile website says I'm scheduled to work this Friday. But I checked mytime at work and it said I was off. I would call ahead and clarify your schedule.