Hey m8, I know this is a year old, but I just wanted to say this: there's no reason to feel embarrassed about an online assessment. Consider that you applied for a graduate role, they probably have a much higher cutoff for those students. Also, these companies are constantly accepting applicants even if they don't need new employees, so timing is critical. If you applied at a bad time, then they may have rejected you for anything aside from a perfect score because they just didn't need the talent then. Good luck in wrapping up your PhD if you haven't already, and good luck in your career as well.