Half a roll? Seriously? A brand new roll? Order a new set (or two). The seesawing will happen until the blades have slipped to the right position in the grips via centrifugal force from the head spinning (one leads a little), spin em up slowly but spin them up enough to straighten them out, if you still get it then you still have balance issues with the blades or the blades are too tight in the grips. What balancer are you using? Do the blades look damaged? Have you tried it without tape on them? If you got wooden blades on that thing replace them with carbon and you'll find the balance to be way better!