Epoxy got cold and thick

No they're not ruined but personally I wouldn't store them outside if possible. My temporary craft room is 10-15 degrees hotter/colder than the outside (depending on if it's hot or cold outside) so I store all unmixed my resins and silicone in an out of the way corner in my kitchen so that they stay in a regulated environment. To thin out resin (just Side A) you just need to "warm" it up to room temperature by sticking Side A in a container of hot water being sure to have the top on tightly and that the water doesn't rise up too high on the side of the bottle. If you want to be double sure you don't get any water in the bottle and have one on hand that is big enough, you can put the bottle in a plastic bag then put it (with the bag covering the bottle) in hot water - be sure to just use hot tap water and not boiling water. If it's hot enough to wash dishes in but not burn your hand then it's just hot enough. Give it about 3-5 minutes to warm up and it should be better soon.