This sentence is false because it does not make sense. First of all, the word fuiste is the conjugation of the verb ir for the second person singular in the preterite tense. This tense is used to describe actions that took place or were completed at a certain point <em>in the past. </em>On the other hand, the word mañana refers to the <em>future. </em>So it is impossible that you <em>went</em> to the discotheque <em>tomorrow</em>
