Turn off all the adjustment layers, so that only "Layer 7" and below are turned on.
Make sure Layer 7 is still selected, and hit Cmd Opt Shift E to create a new merged layer. Convert that to a smart object.
Make a new blank layer above that, and draw a line (using the Line Tool (U)) where the skirting board should go.
Select the merged layer again, Cmd T to get the transform handles, and Option-click at the exact point where the skirting board bends, to put the centre marker there. Then rotate to line the skirting board up to the line you drew.
Delete the line layer
Mask the rotated layer.
Turn all the adjustment layers back on.