Have no fear - your body is actually ready for this one, but your head tells you something else.
There's probably more posts about W5R3 than any other run. And for good reason, cos it's looks odd and scary at first. BUT... it isn't if you take a closer look at the program and how it works.
Just remember that as long as you don't have any limiting physical issues (e.g. clinical/morbid obesity) then *anyone* can complete C25K - it's not a physical test, but a mental one. Your mind ('gremlins') make you think you can't do it (or a certain run) when in fact your body is always ready and prepared for the next run (even W1R1).
Have read of these previous posts:
The myth of W5R3, part 1: healthunlocked.com/couchto5...
The myth of W5R3, part 2: healthunlocked.com/couchto5...
Enjoy!
John