What happens when you press the Next button, when the last question is displayed? Fix this by having the questions cycle back around to the first. That is, the app should display the first question when the user presses the Next button while the last question is displayed.
The Correct/Incorrect label's text does not change when the user switches to the next question. Fix the app so that if the user hasn't yet answered a question, the Correct/Incorrect label is empty.
The quiz is strict about answers. One way to fix this is to make the quiz multiple choice. Modify the app by replacing the text box with a list picker. All questions can use the same list of potential answers.