At the Capulet's home, preparations for the wedding are in full swing. Juliet returns from Friar Laurence's cell with a smile on her face. She "repent[s] of the sin of disobedient opposition" (4.2.17) and begs for her father to forgive her.
Earlier, Juliet had been using language to make one thing sound like another. Now she's lying outright to her parents.
Capulet is overjoyed. In fact, he's so happy that over his wife's objections he decides to move the wedding up a day to Wednesday, which is tomorrow. Juliet and Nurse go to Juliet's room to pick out clothes for Juliet to wear.
It is ironic, and fateful, that Juliet's fake joy convinces Capulet to move the wedding forward a day.