I did the raid alone and also used Gholdengo with a Shell Bell and Steel Tera Type. But my move set was Make It Rain, Flash Cannon, Reflect, and Nasty Plot. Got lucky and got three Nasty Plots set up and then spammed Flash Cannon until I could Terastalize, then I used Make It Rain for some big damage.
I basically just kept either using a heal cheer, or recover. Worst case I'd hit with a flash cannon to get the heal from shell bell. But sometimes you just get super unlucky which sucks, I'm about 14-1 now so hopefully it doesn't happen too frequently for you!
I did this raid alone with zacian steel tera type, max attack and speed, holding rusted sword, used cheer to heal up and wake up, sword dance +4 . Behemoth blade did insane damage with sword dance setup