Right, while i was drunk the other night i ordered a hope floating disc 180mm, disc arrived today and it dawns on me that the disc on my bike is a 183mm:( im running tech m4’s with a B mount, is the 180 going to be ok or should i re-order (sober) a 183?

just buy a different mount.

I would rather sell the disc and buy another one the right size, when looking at the edge of the disc (183) it comes out further than the pad contact area buy a mm or so buy its touch n go is its enough..

shim out the b adaptor to caliper by 1mm?

re-read, shim is wrong way, thought disk was too big!

If all your pad is on the rotor you will be fine, if your pad overlaps the rotor you risk bottoming out pad against pad and also reducing the braking/pad area.

When i look at the disc there is around 1mm of unused surface on the outside, so its actually got more purchase.

I would say get the correct size of rotor to be safe!