SoulPA13,
I think its best to be honest and upfront, do not make excuses. Take responsibility for your past grades and turn it into a positive (I.e you are a more mature and driven individual). Make them see your motivation and reassure them it will not happen again (i.e use your post-bacc grades to support your newly accomplished abilities as a student). Have faith in your-self and the admissions committee will too. They have already looked past your grades by inviting you to an interview, they just want to see your maturity and ability to take responsibility in my opinion. I hope this helps:)
Good luck on your interview!