Yeah the three browns comprise in, out which should be together and the other the switched line to the light from that dimmer. So two browns into common and the other to L1 at the switch. Trial and error will solve it.
Thank you. This solved it. I'm still a bit perplexed because when I originally did it there was definitely 3 wires going to 3 separate terminals...
Maybe an ignorant question but is there any likelihood that by connecting two lives I could be creating a fire hazard? Everything is working peacefully now.