你既然看到問題要提出來。

建議加強跟你的經理的溝通。告訴他一you are concerned that 因為客戶要求不明確，可能會造成rewrok，最後超budget。 suggest put more effort on clarification. However, sometimes, even the client doesn't know what they want. It will be problem for a fixed budget project. You may not be able to resolve, it, but doesn't mean you shouldn't be putting the effort. It may be your manager's job to do that, but your feedback to him is important for him to do well on his job.
你說的：“這個工作是合同，但是按時間給工資很及時。如果以後真遇到問題完不成我好像沒什麽損失” 可能對可能不對，將來有沒有損失誰也不知道。但是既然他們雇你為這個項目做事，你是不是應該負責任的把事情做好，instead of隻考慮自己拿錢有沒有損失？it is your call...