Copy and pasting Masks from Proxies, newby got myself in a hole...

Hello!

Ive been really struggleing with a complex transition that uses an organic rock wall as a break line between two shots.

Im using an oppacity mask, and my main problem is 4k footage melting my (quite new and expensive) laptop, but also masks adding points by accident, rotating the mask instead of moving a point, and crashing when deleting points. 

Im fairly new with premier, but researched/found I could use proxies to improve preformance.

However, like an amature, I imported the proxy file and opened it in its own timeline and did a frame by frame mask in the effects of that timeline. Now im trying to reattach the proxy and I realise I've done it all wrong.

My question is, can I copy that very complex, time consuming frame by frame mask from the proxy timeline (1024x540) onto the raw footage timeline (3840x2160) and recover it?

Ive tried selecting the mask and copying it, but the paste option is greyed out.

I would appreciate the any advice from someone wiser in this! Thanks in advance x