can i mess up the valves in my car?

yes you can and probley have when you take off timeing belt for any reason parts seme to get turned,the cam has to be in proper position so dose the crank and i belive it is another gear that hase to also be in corect position,also you need to know the proper tenson on timeing belt,every thing has to be allined with each other.

yes it is an (interference fit) engine meaning that as the piston travels the valve can try to take the same space as the valve if the camshaft is not properly syncronized with the crankshaft as long as the timing marks were properly aligned when you replaced the timing belt you shouldn't have any problems however if you tried to force the cam or crank to rotate you probably have damaged the pistons and valves.