Lens Correction cropping image

Hello,

so recently I had to document a construction Site at my company.

I used the TTartisan 12 mm Fisheye Lens because I didn't have any better focal length available and also didn't see a necessity in doing a Panorama.
I also knew that the Lens correction for the Samyang 7.5 mm Fisheye would work perfectly with it. 

Now after reviewing the images I realised that Lightroom cuts off a lot of the left/right part of the Image without it beeing visible in the crop window and thus not beeing retrievable.

- I know that the quality will suffer heavily in the sides but thats not really important for this job. -

I found a work around where I scale down the Image in the geometry tab but that completely destroys my image quality.

Is there any way to do this without rescaling everything or destroying my image quality??