If it was a single AA award for the entire return ticket JTR to LHR to JFK then it was either a Business, Premium Economy, or Economy award. If the LHR to JFK segment is in PE then it almost certainly was a PE award which only allows inter Europe travel in Economy. I think the error was booking into Club Europe for JTR to LHR in the first place, so the OP may not be entitled to anything.
The OP needs to clarify how many miles he used for the award, and if it was one single ticket JTR to LHR to JFK, or two separate tickets. That will provide a lot more clarity.