Right answer: parquímetro
A parking meter (parquímetro in Spanish) is a device usually located on public roads (or places like parking lots in shopping centers, for example) that allows ordering and measuring parking in areas defined for that purpose. Its operation is based on raising money in exchange for the right to park a vehicle in a public place, for a certain period of time.
In this context, after parking your car and finish what you were going to do, you have to pay for that service.
Therefore, the complete sentence is:
Después de estacionar mi auto y volver de las compras, pagaré el parquímetro.