You have to go outside with her... I believe that you need to do all the activities (karaoke, dinner, and dinner at another place, cinema...). I don't know if going to buy clothes is necessary.
Viewing post in Shower scene
He already offered you the bathroom for 100k? He first makes the offer, then, if you accatept is 100k; if you don't, 200k... wait a couple of days and go outside alone until you trigger the scene where you give him the money. Then wait a couple more days, go outside until you trigger the remodelation scene, and that's it.