Hello NicoleKendra
In what concerns free travel, the Swiss Travel Pass and the Saver Day Pass do both have the same range of validity. Mt. Rigi is one of the few mountains allowing free travel when holding a pass, no matter which.
So, in a nutshell: Yes, the Saver Day Pass is valid.
Did you purchase the Swiss Travel Pass as a guest or as a registered user (with a login) by any chance? In the latter case, you could find the Swiss Travel Pass order (when purchased from SBB directly) in the list of orders on www.sbb.ch. There, you could request a cancellation without administration fee. You will pay for the cancellation only if you purchased it as a guest, as in this case, the cancellation has to be treated manually by a colleague from SBB, thus labour work is not for free. The total cost for the cancellation would be CHF 20. Perhaps, the amount is negligible, provided you get a new pass for 6 days instead.
Kind regards,
Roland