any idea how to firm it up -can i re-cook it?
I've had that happen. You definitely didn't cook it long enough. I've never tried recooking it, once you add the coconut and pecans, I wouldn't think that it would have the same effect. I've added more coconut and pecans, and that helps a little.
It's a pain trying to get that right, almost like you can't tell if it is think enough, but once you get it to the right point, you'll absolutely know that it is thick enough.