Just a comment, it sounds like you are kind of concerned about going to grad school right away, and ambivalent about spending time working after undergrad. As someone who also has multi-disciplinary interests and experiences, and ended up in the most perfect grad program possible for me, I feel like I should put in my two cents that it is really best to take your time figuring this out. I agree with fillyglory above that you should be able to do well combining the different fields you're interested in, but I also need to caution that figuring out the best way to do that takes a lot of time, research, and soul-searching. There is literally no down side to getting a job after undergrad, especially in your position where you would definitely be able to get a research or professional job. As you mentioned, you would have to then figure out what sort of job you want, but the thing is choosing a job is much, much, much less of a commitment than choosing a grad program. It doesn't matter if it turns out not to be in the field you ultimately choose to study in grad school, it will still enhance your application. In fact, I'd say that the one thing missing from your application right now is long-term experience (a year or more) on a research project. This is actually really important, it will show grad programs you are able to commit and stick things out, and likely give you a higher degree of independence and ownership of a project than when you're only in a lab for a few months (something else that admissions committees look for). Your best move might be to look for a research assistant position or something like that- they are generally very understanding about you leaving to go to grad school, and it tends to make for a great LOR.
Or, you might figure everything out a lot quicker than I did and go to grad school right away. I'm just saying you shouldn't feel like you have to. For where you are right now, I recommend taking a few steps back to assess and prioritize your interests. For example, list out all the fields that appeal to you, then start asking yourself what it is about them specifically that you enjoy. Is it the subject matter itself, the particular approach, the purpose it's working towards, or the way of thinking involved? For areas where the subject matter itself appeals to you, can you rank those subjects by how much you like them? And so forth. If you have some sort of idea of the subject matter, approaches, and research purposes that appeal to you most, you can start looking at programs with a better idea of what you're looking for- simultaneously broadening and narrowing your search. (So maybe you really like biology, but only a certain type of research within biology, so only a subset of programs actually have that research. Within those, only a few professors will be working on it. However, maybe in a field you hadn't thought of before there's some professors employing an approach you really like towards research that addresses biological problems) Of course, I just summarized a really complex process that I went through over more than a year in a few sentences, so don't take that verbatim. If you want more details, feel free to ask.
