Your marks probably got you the interview so they wont be worried about them so much. What they will be interested in is your character. They will want to know if you have good communication skills and whether you can work on your own and as part of a group. They will particularly want to know if you really want to do their degree - have you researched the field do you know what they do etc. They will also want some examples of where you have acted like an engineer (e.g. solved challenging problems, built something etc.).