In this context, the second sentence expresses a hypothetical situation contrary to the current reality (since it's raining and you're not going out).
To correctly convey this counterfactual condition, the sentence should use the past perfect tense in the 'if' clause and 'would have' in the main clause. Therefore, the correct construction is:
"We would have gotten wet if we had gone out."
This structure aligns with the third conditional form, which is used to discuss hypothetical situations in the past and their possible outcomes.
The third conditional is formed with 'if' + past perfect, followed by 'would have' + past participle.
Thus, the corrected version of your sentence is:
"It's raining, so we're not going out. We would have gotten wet if we had gone out."
This accurately reflects the hypothetical scenario of going out in the rain and its consequence.