you're not getting into any SMP with a BCP of 2.5, most programs require a minimum BCP of 3.0 before they'll even look at the application.
Also the SMP and AADSAS will average ALL retakes into GPA. Believe me, I retook a class twice: 1st time C, second time C+, third time A-. I would have been much better off just getting 2 more As.
My advice would be to stay for as long as necessary to get your BCP to around 3.2. Then you'll be able to do a SMP, normal master's, or maybe right into DS if you ace the DAT.
In the end, no adcom will care if you stay in undergrad for 7 years as long as the the additional time shows a VERY UPWARD TREND.