You would need the 32-bit version. 64-bit software can never run on a 32-bit platform.
Having said that, it is time to upgrade your 32-bit version to 64-bit (by purchasing a new license/copy).
Going forward you will be running into this issue with more and more software since 32-bit these days is a dwindling platform.
I am not so stupid that I would have tried to run the 64-bit installer on a 32-bit OS - I've been "playing" with computers since the days of CPM and DOS2.0, have gone through all the iterations of windows and also toyed wiith OS/2 for a while.
While I appreciate the benefits of 64-bit architecture, I really do not want the b@ll-ache of having to rebuild the machine and reinstall all the apps that are in use, some of which won't run on 64-bit so I'd have to install a VM to run them.
If WhatsApp has released a 32-bit installer then it should work and they would be helping the user community by having a little bit of support out there.