Assalamu alaikum I took out an interest-based loan in the past. Later I sincerely repented, but I’m still paying it off with interest. Am I still sinful while repaying it? At the time, I was unfortunately ignorant of the ruling.

Your sincere repentance lifts the sin of the past, in shā' Allah, especially as you were ignorant of the ruling at the time. Continuing to pay what you are contractually bound to is the consequence you are working out of, not a new sin you are choosing, but you should free yourself from it as soon as you are able and avoid renewing anything of the kind.