بسم الله الرحمن الرحيم
When a musafir intends to stay somewhere less than fifteen days then he remains musafir as per the Shariah no matter if he has to stay there for many years by changing his journey plan repeatedly. Hence when you for the first time intended to stay there from 16 April to 28 April that is less than fifteen days though you could not carry out your intention and your stay period lengthened, yet you are musafir. Thus it is correct for you to do qasr while staying there.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.