Installing a new bra in cold weather can be next to impossible. The vinyl needs to be warm to stretch enough to fit. If you don't have a heated garage to use, you might try heating it with a hair dryer or (carefully) with a heat gun.
:Word: Unless you are installing the bra to cover up existing damage, do not run full time with one on the car. You may think that it will protect the paint, but the reality is that they do much more damage than good if left on for long periods. I will use them for long road trips, but always heavily wax the front of the car before installing and remove it immediately upon returning. Even then, there are marks left in the paint at the stress points when I remove them that require polishing compound to get out. I had a new car customer at the dealership where I work put on a brand new factory bra, take a 3,000-mile road trip, and remove it to find that it had worn completely through the paint in several places.