I have tasks that need to be done on multiple projects so I used the Add to Project and added it to each project. Now if I complete one of the tasks on one project, it then will show that I completed it on another project which I don’t want. Is doing add to a project not an option?
What you did is known as “multi-homing” one task to appear in multiple projects, which is useful but not for what you need it seems.
One option is just to duplicate the task (right click on the task in the tasks list and choose Duplicate) once for each duplicate task you need; you can put each one in its own project if desired.
You can also search the Forum here or the Asana Guide for Assign Duplicates for another option.