Hey young man,
You are still young and you have plenty of time to better yourself and make yourself more competitive. Keep doing what you're doing. Graduate first ! Get a job in the ICU in a big level I trauma teaching hospital (For Example: hospitals where you take care of the patients with A-LINE, Central Line, (or pt need to be intubated, ect.) on DAILY BASIS ! You DO NOT NEED to be on the Ward, or Step-down Unit first (if anyone ever told you so..)
When you are done with nursing school, please SHADOW and also contact the CRNA Program Directors where you want to go, and ask them how to be more competitive and keep in touch with them, allow them to guide you and listen to what they tell you. Show them you have a Fire in your belly that this is what you want to do. I wish that I would have know what I wanted to do when I was as your age. It's not easy, and please understand that while you have done several things to strengthen your application, you are competing against many applicants who have done the same. This contributes to a very competitive field, so the more you can do to "rise to the top", the better. But its totally worth it when you receive a phone call from the director to invite you to join their program. The bottom line is : You might need to retake the science courses you received -B; however, first thing first, graduate and get a good ICU job !
Continue work hard and focus on your goals toward nurse anesthesia. And when things get difficult, do not feel discouraged, just hang tight and you will get there somedays !