Been thinking about how to improve. Found a great guide here, and can see that I'd not invested enough time in the session. Also realised how different this was to using any other toy. This definitely isn't like a vibrator. It needs time and attention.
Decided to try out the Helix again, but this time just to get used to it. Slipped it in for an hour, and got on with an otherwise normal Sunday afternoon.
Caught myself clamping down on it by accident. So my body is learning what it's about.