Noobie question: Are "out and back" routes, ie return by the way you went out, acceptable for DIY certification?
Yes. I have several in the RRTY Emergency Armoury.
As long as minimum distance between controls is adhered to, and you don't have much more than 50km between controls, it works.
Here's a couple of mine:
Swaffham -> Wisbech -> Stamford -> Wisbech -> Swaffham
Swaffham-> Newmarket -> Saffron Walden -> Bishop's Stortford -> Saffron Walden -> Newmarket ->Swaffham
HTH