I did W1w3 today, and it was great!

W1w2 really sucked, so I was pleasantly surprised by today.
I think I'm ready to move on to Week 2, but I have a question... I walk at 3.4mph and jog at 4.5mph. It gets my heartrate up and I'm tired at the end of my workout. I could jog at 5.0mph, but it absolutely exhausts me, so I don't think I could start Week 2 if I jogged at 5mph. Would it be better to keep at 4.5mph and start Week 2, or do Week 1 again, but at a faster speed?
I've only finished one week of the program thus far, but I feel so accomplished! You guys really impress and inspire me with how you've progressed.