Stop Gap is a temporary or a makeshift arrangement unless a more permanent solution is put in place. Stop gap arrangements ensure that there is no disruption in the functionality or the service.
Quick Win is a visible improvement which is implemented soon after the project starts. It keeps the team motivated and they do not have to wait until the project end to see the results. These are also called the 'Low Hanging Fruits'.
An application-oriented question on the topic along with responses can be seen below. The best answer was provided by Somrita Chatterjee on 31st December 2018.
Also review the answer provided by Mr Venugopal R, Benchmark Six Sigma's in-house expert.