I have a toyota previa that I changed head gasket on now I can't get camshafts line up right

Can you be more specific on what kind of problem you're having? Do you know that one of the cams has a 'scissors' gear and needs a set screw installed prior to installation? (spring loaded)

Note: Helping US to help you goes a long way here at this site. I have a lot of information on hand to help out. What year? Supercharged model, or regular?