Hi Angie,
I am currently going into the week 7 and I had exactly the same experience as you are having. I stressed about the 20 min for almost 2 weeks. My body was ready to do it but my biggest challenge was the mental block that I have never ran for that long in my life. I got on the treadmill thinking that I will just take it a minute at a time. I knew I could do the 8 minutes since I already did it couple of times and after that I just kept going. When I hit 10 min I thought it is only 5 minutes to do 15 min and once I got to 15 min I was not going to give up because you can definitely do 5 more minutes. I had a hard time at about 17 min completed but I was so close I thought if I don't complete this now I will have to start all over the next day and that kept me going. The feeling at the end was fantastic! It is all about the mental challenge. I try to break the long runs into "doable" blocks in my mind. If I tell myself that I will run 3 minutes I will die at about 3:10 whereas when I trick my mind it works. I just did the 25 minutes 2 days ago (and it was much easier mentally than the 20 min) and now I am stressing again about the next 3 weeks of no walking breaks! There are couple of threads that are in the weeks 7 and 8 that talk about their experience. It really helps to see people feeling exactly as you do and acing the program in the end. Good luck!

I was too. The 20 minute run with no walking was great for me. I sometimes found it difficult to resume running after the walk break. I went through week 5 in great shape and I am now in week 8.