The correct option is
C didn't
Sentences are said to be in the subjunctive mood when they express states of unreality like a wish, desire, possibility, emotion, etc.
The given sentences expresses a wish, so it's in the subjunctive mood. Also, the verb 'wish' expresses the present desire, hence the tense.
Option A: 'Won't' is a verb that expresses a future event in the negative (will not). The verb 'won't' is not used in conditionals (subjunctive mood), hence this isn't a suitable option.
Option B: 'Can't' expresses possibility as opposed to wish.
Option D: 'Shouldn't' expresses obligation or duty. The verb does not relate to the subjunctive mood 'wish'.
Hence options A, B and D are incorrect.
Option C: 'Didn't' is often used in sentences like these, when the person expresses a wish that something was not the way it is. Also, we use past tense forms (like 'didn't) to talk about wishes and desires in the present.
Hence option D is correct.