68 Camaro Headliner - How much stretch?

[cad]

Hi guys,
I am in process of installing a stock headliner in my 68.
I have it mocked up/stretched and held in place with binder clips. I have the DAP Weldwood contact cement.
I have read that the material will shrink with time and natural heat.
If that is true, how much stretching is enough when stretching the fabric prior to gluing?
If that is true, are there also any short term methods for shrinking any areas that dont quite lay up nicely, such as steam and then a hair dryer, or?

Thanks in advance,
Clark