Can you arrange a time to sit with your manager to talk about expectations? It seems you have been thrown in very quickly with very little support. It can take time for you and your manager to learn the best way to work together and so hopefully you can work it out.

Could you sit down and talk about the project and any future deadlines? Explain that you want to be able to work effectively and to do that would like to have the deadlines communicated as early as possible. Hopefully it is just that your manager doesn't yet understand the way you like to work and that they are open to discussion about different ways to manage things.