Trending @Cognizant; I've been puted into a fresh project and manager hold me whole responsibility for the backend, which I have only little experience working on the desired code and technology.

Previously I was under the senior dev who was my mentor and guide me where ever I got stuck, but now in this project I'm the only developer and they made me sme also ,as the budget of the project is pretty low, what should I do in this case should I tell the manager who deployed me in this project that I'm not that much compatible for the position you are setting me into? Please guys give suggestion I'm very confused and tensed, what to do...