Thailand > Shanghai > Costa Rica

I got Costa Rican passport and a residence permit for study in China that's valid until July 31st (I overlooked this when i bought the tickets).

I was planning to go to Thailand at the end of July, then fly back to Shanghai to leave to Costa Rica on August 3rd, because the flight was cheaper this way. I've only bought the ticket from Shanghai to Costa Rica, so when I get the one from Thailand to Shanghai, it will look like China is the final destination. What do I need to be able to stay in Shanghai for a day or less if my ticket doesn't show Shanghai as a stopover?