The 64 bit will be on a separate DVD. You should have got 2 DVDs if you bought a retail W7 version.
Did you just get one DVD - an upgrade from Vista 32bit to W7 DVD?
You could try downloading the W7 64bit .iso and burn your own DVD from the link on Heidoc.net - they are the official MS download links ClickHere scroll down the page to the English(USA) SP1 U versions. The x64 is the 64bit and the x86 is the 32bit.