The problem is that you're using integer division right here:
(correctQuestionsForAttempt.Count / dvAttemptQuestions.Count * 100)
With integer division in a case like this, you'll always end up with 0 or 100.
This will work:
(100.0 * correctQuestionsForAttempt.Count / dvAttemptQuestions.Count)
Also, from what you describe, you want a Ceiling
function (think of it as rounding up), not a Round
(rounding to the nearest integer, with options on how to round midpoint values).
int userScorePercentageConvert = (int)Math.Ceiling(100.0 * correctQuestionsForAttempt.Count / dvAttemptQuestions.Count);