GetLogicalDrives() enumerates all mounted disk partitions, not physical drives.
You can enumerate the drive letters with (or without) GetLogicalDrives, then call QueryDosDevice() to find out which physical drive the letter is mapped to.
Alternatively, you can decode the information in the registry at HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices. The binary data encodings there are not obvious, however. If you have a copy of Russinovich and Solomon's book Microsoft Windows Internals, this registry hive is discussed in Chapter 10.