Garage Footer???

[Beamster]

Your footings are not huge. Part of the purpose of the footings are to support the wall forms.

And the frost requirements are to the bottom of the footings but you need to be on undisturbed (original, not previously dug), inorganic (no roots, peat, etc) firm soil. Some soils are sensitive to wetting and working, so you might need to skim off additional material if it rains on your excavation.
And just compacting the top of loose soil does not prevent the soil below from settlement when it gets loaded by the building and floor loads.

Suggest you use not less than 10" thick footings but 12" is pretty much a commercial standard.

For the wall projection above the finish ground surface, your local Building Code has a requirement on how far ant wood framing needs to be from the ground surface, so check that out.

Don't skimp on your foundation. Remember the tower of Pisa.
Those are mistakes that you're not going to want to try to fix.