Explanation:

- The sentence begins with a conditional clause: "If you promise...". This indicates that the following clause should express a condition that the speaker wants the other person to agree to.

- Option 1: Not to get

- This is the correct answer. It maintains the grammatical structure, as "promise not to [verb]" is a standard way to phrase such a condition.

- Option 2: Get out

- This implies dismissal and does not fit contextually or grammatically in this sentence.

- Option 3: Not getting

- This is grammatically incorrect here. "Not getting" would require a different sentence structure.

- Option 4: Not get

- This is ungrammatical in standard English within this context.