For starters, do not increase the torque! You are stressing the studs and you run the risk of of stud failure.
Not safe! It sounds like your wheels are not hub-centric (don't fit snug on the axle end). Your car does not have the same center bore as a 350z. If it is an aftermarket wheel it would require a center ring to fit safely. It can't just center on the lugs. You need to get back with the shop that sold you the wheels for the correct (safe hardware) if it's available. The stock 350x wheels have an even smaller center bore than your car so I'm at a loss to know how they would even think the wheels are going to fit safely.