I think what you are trying to say: Are you sure we haven't forgotten anything? Make sure you don't forget anything. Is this correct? If so:- The first one is a question in the present perfect - an action that began in the past and has an effect in the present. The second one is in the present simple and is a simple instruction or advice for someone. Hope this helps :-)

These both seem like informal questions. It would usually be "Are you sure" instead of "you are sure". However, I have heard people say "You are sure we are not forgetting anything?". I think it would be considered slang or improper though. I do not think you should ever use "don't" in this sentence, because "don't" is a contraction of "do not", which is for future tense. The question (I think) you are asking would be either present or past tense. Hope that is clear and helps!

TOM: You are sure we are not forgetting anything? (commonly used) EXAMPLE: Tom is going on a trip with some friends. He is not certain that they have packed everything they need. His friend Jane is a very responsible and reliable person. So Tom checks with Jane. Jane says they have everything. But Tom wants to be absolutely certain, so he asks her again: "You are sure we are not forgetting anything?" TOM: You are sure we don't forget anything? (rarely used; maybe in a science fiction movie) EXAMPLE: "We don't [ever] forget anything" is about a personal habit. Tom and Jane have incredible memories. Their friends say about them that they don't forget anything. Tom has his doubts. For the first time in his life, he thinks he has forgotten something very important.