ELISA for mouse blood Ghrelin

I want to measure serum Ghrelin levels in mice samples. I collected serum about 3 weeks ago, and froze it at -80 degree. I only received the ELISA kit 2 days ago. The kit says the sample should be acidified to 0.05N with HCl after collection, and kept at -20C for later use.
May someone with some experience in Ghrelin analysis advise me if its now a 'non starter' to go ahead with the analysis having made the mistakes of not acidifying and keeping at -80C. Do you think it has gone all wrong already? I really don't want to waste the kit because I had trouble getting it, and its a 'one time use'.