bsharpe269 has covered some good advice, so I won't reiterate.
I didn't start out as an anthropologist, either. I am now a holder of a MSc in an anthropology subfield, having completed the degree in a pretty major UK department. Please keep this in mind, as it might skew my experience in relation to yours. I did a BAH in History and Classics (there wasn't an athro department at my university, but Classics had archaeology classes so I loaded up on those), a MA History in Canada and my MSc in an anthropology subfield in the UK. I've also done a few digs in Italy, outside of field school. I know this advice is solid because I was offered a major fellowship at a well-respected anthropology department for PhD study last year. I didn't take it, but that's neither here nor there. You can do this. Here are my thoughts:
I found that what they're really looking for is your ability to do the anthropology work and have the right experience behind it all. So, even though I came from more of a history background, I had the interest, and had demonstrated some basic archaeological training. So, you should definitely take more than 2 anthropology classes if you want a better chance at getting into anthro for grad school. Start trying to beef up your anthro credentials now; volunteer at a local museum helping with an anthro collection, offer to help a prof in anthropology with some grunt work on a project, etc. See if you can do an independent study project as a senior, and tailor it to be anthropologically heavy. It's going to be hard - nobody said it would be easy here in academia - but you can easily become a very good candidate if you work toward it.
Here's the good news: you can spin a combination of classes from related fields into a good background and offer of admission because social sciences are becoming interdisciplinary (and use that term when explaining how your current and future experience during undergrad relate to what you want to study and why you fit into an anthropology department). Sociology, history, anthropology, etc., are all interrelated, and this is your crux.
The rest? It's luck and dedication.