Lying in a job interview

My question is regarding lying on a telephone interview for a university application. I had a telephone interview for computing course. I initially applied for a different course for which I got accepted with an unconditional offer. When I decided to change I had a telephone interview and the Head of department asked me as to why I didn't retake my GCSE Maths Exam as i had a D. I don't know how was it impulsive or due to nervousness I said that I was working full time. So he said ok and asked about my other qualification which is the main one BTEC I.T. He was satisfied and gave me an unconditional offer. So the lie is that I actually have retook my GCSE Exam and Got the same Result. I was certain that I had put it on my original application but it seems I didn't. To my shock I said the lie. I was actually working though pretty much full time. On Registration the Uni only took my BTEC cert. Am I sinful? Will my earnings be Halaal?