Have you actually checked to see what G.P.A. is the minimum accepted at the grad school you want to go to? I know you want to be as competitive as possible, but you might actually be pushing yourself too hard. Gee, some folks would be absolutely thrilled with your record. I know I am impressed.
Don't recommendations and G.R.E. scores count for something in the admissions process as well?
I happen to know not all other schools would be just "mediocre." I agree not to just put all your plans (eggs) in this one basket. It would be risky for anybody to just apply to one grad school anyway, even with a 4.0.
Conclusion: Your future is not "ruined." Please don't make it into a catastrophe when it truly is not. What grad schools do other English professors have their degrees from, especially more recent graduates? I bet they all didn't graduate from this one school.