Did you modify it at all when you first start?

It seems like for me to keep going 90 seconds of walking and 60 seconds of running for 20 minutes is just TOO MUCH for me.

Give it a go, see what you can do, and then evaluate from there.

I am only on my second week at the moment, and when I started last week, I couldn't complete all of the runs until W1D3, when I got through every running part . And you can always re-do weeks. My plan is if I struggle to complete a stretch, to keep doing this week/day until I can do it.

The trick, I've found, is to go slow. At the moment my aim isn't distance, it's time. So when I'm running, it's more of a slow, bouncing on the spot kind of jog (lol).
You could start off just walking for 20 minutes on a flat surface, and build up to the C25K. I started walking at the beginning of this year, for a distance of 5K, and at first I found that that was enough for me, but now it isn't. So I'm now trying C25K. So far my un-athletic body is really enjoying it.

I hope that helps =)

Lol, I meant to say it is too much for me, I started today and I just seem to need a longer break than 90 seconds from running.

Walk it then...? lol, that's what I did. I did the first few running sectors, and walked the last two. First day is hard. Then 3rd day, I managed to all the jogging parts.
It's something that you can build up to.

It may be more manageable if you do a slightly slower pace. In general you should be focused more on going for a certain time OR distance over pace. If tweaking the pace doesn't help, just do what you can. You can repeat week 1 as much as you need, and maybe at first just plan to do every other run. And c25k is just one path to get there, but it's not the only way.

Sparkpeople has a couple of different plans too, including an 8 week plan where the first week you walk 4 min, run 1 min. My local running store does a 10 week beginner's running group/class for a 5k, and their first week they do run 1 min, walk 3 min. In the end they're still in the same place, ideally anyway.

I just looked at the one on sparkpeople, sounds like my kind of thing!

You might consider spending more time walking. Currently I'm back on a basic/easy program (after injuring my knee) so I'm doing a 10 minute warm up (power walk) then 1 minute running, 3 minutes power walking, then repeat 6 - 7 times so my total workout is around 45-50 mins including cool down time.

When I first started C25K I modified it so that I would only run as long as I could then stop and walk for a few minutes, then try again. It might have only been 30 seconds the very first time, then the next it was 60 seconds and so on. Then my aim was to make it thru an entire 'power song'. Not very scientific but it worked for me.

You may be going too fast. When I first started the C25K program, I tried running at 5.0 mph and I had to downgrade it to 4.0 (the pace at which most people walk, oops). I modified the program as I went on, I think I repeated every single week because I just wasn't ready for the next.

You can do it

I felt it was too much for me at first but I did it anyway and it worked out just fine. Stretch a lot both before and after and remember to regulate your breathing. Pay attention to how your feet are hitting the road/treadmill - make sure you are not pronating and if you are, correct it. This gave me a bit of pain at first, and I still have calf pain but I think that's because my muscles hurt.

I'm on week 5, and only now have I had to modify it. But everyone is different, and our bodies are built differently. If you feel like you have to modify, I would also say go slower - when it's too hard for me I go at 4.8, and I've never ran faster than a 5.1. People always say it's speed that kills beginner runners.

Overall, the program has made me feel great after the runs.

If you struggle with a week on C25K, modify it and repeat the week until you can complete it before moving on.

But most likely you need to learn to run slower. Think jog not run. Slow Slower Sloooooowwwwwer. The biggest mistake people make with C25K is get sucked into thinking they are supposed to be able to run a certain pace.

Ennay is right... I am only at the end of Week 2 but I found when I got winded I just slowed down and I was able to finish.