Help, measured pitch wrong, halfway through tiling

[des606]

Shed build

Calculated a 12 degree roof at 20 degrees (don't ask , I don't know how!) , so went ahead and got slates with a minimum 20 degree spec.

have now done half the slating, and realise I'll have to dump slates and start over or raise the pitch.

I think with a load of supports on walls ( all wood build) it may be possible, if acro props can be adjusted to raise the roof while in situ??????

Or can they just be positioned to bear weight rather than being able to raise a load??

Thanks, Des