Chris,
whether it was your fault or the cyclists fault, you’ll get flamed on here regardless, but the best piece of advice I can give you is to examine what you did, and ask whether you could have prevented it, for instance by choosing a different place to do a 3 point turn, or even not doing a 3 point turn in the road – was there a gateway or anything you could have used to turn round without blocking the road?
It’s often not about who’s at fault, but about what you can do to avoid an incident. Unfortunately this comes with experience, which you’ll get over the coming years (sorry if this sounds patronising, but I am teaching my youngest to drive at the moment, and it’s surprising how different his attitude is to mine, even though I have a bit more experience than him….)