You were married in the UK so the marriage certificate you were given at the ceremony is the certificate you need. It should be perfectly acceptable.
And good on you getting more than one copy! You never know when you're going to need it over the next few months/years! 
i phoned the consulate in NY to hear their list of required documents for the spouse visa.
and it lists the copy of marriage cert. bearing a raised seal. i then phoned the registry office where we were married and was
informed that no registry certificates in the country are issued with a raised seal.
so now, i am convinced (at 11.40am) i am going mad
i think i will end up phoning the consulates (again) to ask about this...
another thing that raised a bit of concern for me is this -
my address at the time of the marriage is listed at my partner's UK address. (since that is where i was staying)., might this cause an problem(issue) as at the time of marriage i was not permantantly residing in the UK?
(i certainly hope my inpending insanity over all this is normal!!)
thanks again!
-trish