If you feel that this is a bait-and-switch operation, and you're uncomfortable with it, then pursue new employment immediately.
Furthermore, if you've only been with this job for a few days or weeks, then don't feel obligated to even mention it at interviews.
If you've had the job for a bit longer, then be upfront with interviewers and tell them that the job was not what you expected.
@HLGEM's answer is incorrect to the extent that you're never under any inherent obligation to stick with a job. Bear in mind that the following pieces of advice are not mutually exclusive:
- If a job isn't helping you advance, then seek new employment immediately. If you don't care about your career development, then nobody else will.
- On the other hand, try not to move around too much because employers will doubt your ability to deliver and finish.
If you're mindful of both, then you'll be just fine.