Your biology degree will definitely be an advantage in the application process. I can't speak from experience as I don't start CRNA school until August, but I know a few people who hold a degree in either biology or chemistry and applied, and all were told that it was a mark in their favor.
I felt the same as you in regards to much of the science content in the BSN program that I attended. While I learned much, it could be rather disjointed, and I felt that many of the professors didn't have a very deep understanding of the content. Advanced practice curricula is obviously much more focused on a specific area, and CRNA programs in particular stress chemistry, microbiology, and advanced pathophysiology.
The general consensus among people that I talk to, both CRNA's and students, is that most programs love applicants who have extra coursework in chemistry as well as biology. While I have neither, I was told that my experience working as a certified pharmacy tech was a plus. Obviously there are many other factors that influence admittance, such as GPA, ICU experience, GRE scores, and the interview itself. Ultimately your strength and background as an ICU nurse will be the strongest criterion for admittance.
Your nursing GPA should be fine, especially along with your solid overall GPA. Most programs weigh an applicants GPA several different ways, such as overall GPA, science GPA, nursing school GPA, and the last 60 hours GPA. If you're deficient in one area, you can always compensate in another, such as making a high score on the GRE, obtaining other certs such as the CCRN ( which is mandatory for many schools), taking on leadership or research roles in the ICU, or taking a few extra classes to bump up your GPA in the last 60 hours category.
I hope this helps, and good luck!