Lubaina.
When you say you have made a huge ammount of mixture are you sayng you have doubled the recipe or more?? Not the best idea as a single mix will be a more reliable result.
No, I wouldn't suggest you add more PVA glue. Probably more Cornstarch and re-cook it checking every 30 seconds until you have the right result.
As this is something I haven't experienced it is difficult for me to advise you.
Trial and error will be your test!!
Good luck.
Katy
There is a simple solution is that spread vaseline or any cold cream at surface and into moulds. Let it dries in natural way and you did not make trouble for me but it is my pleasure to help you.
I am so glad to hear that your cold porcelain came out well and you made some creations, at last I feel good that my efforts not went in vain. Waiting of your video.