Emily, was the foam mattress compressed? If so, it could take a little bit to de-compress, accounting for the extra overhang. Most mattress people don't deal with compressed foam beds, but this is common if a bed has been compressed. It will be a few inches wider until fully expanded.

That said, I know in the mattress industry in general that measurements are not EXACT. Most warranties you read will account for and inch or so in either direction, width, length.

That shouldn't be. Measure both length and width of the mattress and the boxsprings. Contact who you bought it from and ask them these questions. Is it 2 inches all the way around or just on one side/end? Two inches all around would make the mattress closer to a queen. "Normally" we would see a mattress to be smaller than the foundation. IF the mattress and boxsprings are from the same manufacturer they should honor the warranty. Overhang is not ideal.

I agree with Ernest….you want the optimal conditions for better wear. That overhang may impact the longevity of the mattress.