It's a year after your post and I'm not sure if you have made any choices yet, so I wanted to share my experiences with you:
I majored in biology because I grew up outdoors with some great environmental experiences in the 1970's in South Florida and I grew into a commitment to saving/restoring the environment. When I was an undergraduate, there were no environmental science courses at my institution, so I took geography, anthropology, and marine science courses to supplement my biology. I worked for several seasons as an Interpretive Park Ranger with the National Park Service and one of my best friends kept at it until he got a full-time position. His entire 20+ year career in the NPS has allowed him to get up from behind his desk to offer inspiring environmental education programming to many different audiences.
Meanwhile, after returning to universities for Masters degrees in biology and in education, I have worked as an environmental educator at parks on city, county, and state levels, and if it wasn't for a move for my husband's work at the height of the 2008-2009 economic collapse, I feel that a park job could have offered me a long-term sustainable career at the state level (but it depends on which state you are in and your flexibility to move). I am not sure if you have worked in a park system as an outdoor educator, but I think that adding environmental education certification through the NAAEE or your state affiliate would help you gain skills and offer you experiences to try out environmental education. I am taking the Arizona Association of Environmental Education's Environmental Educator Basic Certification Program now. Good luck!