[eenieMINI]

Nah.. this is a common new user error.. Using the method you described WILL change your today background but it is independant of TouchFlo3D... so what you really want to do is be in TouchFlo3D .. where you see the sprint clock and appointments etc.. slide over to your "Settings" Tab (Not Start/Settings) and then you'll see an option for "wallpaper" click that and you'll find what you need.

Be advised this will change ONLY the first "clock" screen. The rest of your screens will have the default wallpaper.
If you want to change this you have several options, install a premade complete theme (check the themes forum under VGA themes), create your own theme using the various manila editing programs, install background4all or panoramabackground setups, or be happy with just clock screen changing.

Read a few of the threads about posting today screens (there are links to how/where to get setup), search the pano thread and background4all thread as well as corner clock thread, check the PRO forum too because those same setups (manila looks-wise) are interchangable, and be sure to go to the themes forum and read the sticky abuot how to customize manila by goodthings2life its very helpful..

My advice, to read for a few days to be sure you know which way you want to go.. these customizations have come a long way since September release of our phones (and earlier) so there are quite a few paths to choose from.

Good Luck and be sure to ask for help, there are many helpful and knowledgable geeks on here!