Upvote:2
There are three options:
But to find out you need to call the airline. Go with what the airline tells you to do.
And better call sooner rather than later.
If it is the first, 'cancel and buy a new ticket' and the travel agent entered the information wrong, ask them to pay for the extra cost. (Likely they will not pay or at least not all but you do have a chance they will pay.)
Whatever you do, do not wait till the day of the flight as getting things corrected on short notice is harder and can be very costly.