Thank you for your work!
Don't be so hard on yourself. I think they were just trying to encourage the original translator because they were hesitant to continue due to their slower pace; you just got caught in the crossfire. If it weren't for this situation, I don't think anyone would have said those things, because I don't think what they were saying was as a criticism of your work.
Don't get discouraged. You did a good job; I wouldn't have realized it was your first time doing this. It's a shame your first experience was under those circumstances.