Using Nikwax to rewaterproof a Bivvy Bag - Carinthia Observer Bivy AKA NL Observer Bivy

I bought a NL Observer Bivy bag (also known as the Carinthia Observer Bivy) and it has lost it's ability to be waterproof. This could be because it was washed incorrectly as Goretex is supposed to be reliably waterproof. My web research led me to believe it might have lost it's DWR layer due to washing so I bought some Nikwax tech wash and Nikwax waterproofing spray to try to restore the waterproof layer. If I am going to use this to wild camp it needs to be waterproof.