[MartinOM28V]

I think you're gonna need a new one, because the saddle is so critical to transmitting sound from string to soundboard. But as a temporary fix you could try one of these homebrew methods:

1) Brush thin coat of Z-poxy or similar epoxy/super glue on the back side of the saddle, and let it fully cure before inserting.

2) Put a thin strip of metallic tape on the back side of the saddle

3) Take one of those flat cocktail toothpicks and, after installing the saddle, try to wedge the end between the back of the saddle and the saddle cavity. Break off the excess. Start in the middle then put another little wedge on each side to keep saddle straight.

As above poster says though you really need to chalk it up to experience and grab a new blank, but maybe one of the above will help you get by in the meantime.