Everyone talking about the gap but nothing about the huge problem you now have.

Aluminum doors are a big ole 0 for insulation. They let cold and heat through them like they arent even there. You need to look into some insulation boards for them and install. That will definitely help with the cold in the garage.

Go to Home Depot, head to the caulk section and look for clear silicone. There should be one there in a toothpaste style tube. That should work well and the clear finish can be good if smoothed.