If you rotated it CW by "x" degrees, you should be able to rotate it CCW by "x" degrees and get it back close to where it needs to be. The crank is at TDC+50 to give you the most clearance between valve and pistons. IOW, its a bit of wiggle room while putting on the new belt and to keep from damaging the valves if(more likely when) the cam snap-rolls due to spring pressure. How far, in degrees, do you estimate that you accidentally rotated the cam? You do realize that the cam will snap-roll? You may only be fighting the spring pressure to return it to original position, which is fine.
Take a look at this thread. Should be close -> http://us.lexusownersclub.com/forums/index.php?showtopic=61372&st=0&p=394040&hl=how_to&fromsearch=1entry394040
I put the crankshaft back, and confirmed that the Crank pulley was indeed at TDC+50 position.