I would keep on going. Some days will be better and some days you'll be slow and that is totally ok. Most people will repeat a week if they really feel they could do better, or if they skip a day, were sick, etc. I would say finish off the 3 day of week 1 and see how you feel about your progress. Good luck!

Lots of posts on here encourage you to run as slowly as you possibly can whilst still maintaining a running movement. The speed will come later. There may be all sorts of reasons why you found the second session harder: tiredness, TOM, time of day, when you last ate etc etc. I would press on and keep progressing until you can't do what the session asks for and only then repeat. I have got to W4D1 without repeating any session and although some of them were challenging I haven't backed off going up a level. Sometimes I preempt the next week by extending the final run of the previous week by enough to match the next challenge up as it gives me confidence to embrace the next week.

Good luck with your regime!