💡 Detailed Explanation
The correct choice is Option 2: 'Yeah, sounds good. Let's go.' The speaker is using an informal invitation ('〜ない？'). To agree enthusiastically to an invitation, one says 'うん、いいね。行こう' (Yeah, sounds great. Let's go). Option 1 ('うん、行きたくない' - Yeah, I don't want to go) is grammatically contradicting (answering 'yes' to 'I don't want to go' is very harsh and conflicting). Option 3 ('うん、見なかった' - Yeah, I didn't watch) uses the past tense for a future invitation, which makes no sense.