If they were like that in the cup I'm thinking it was just because of his terrible conditions, do water changes really regularly in that 1 gallon and make sure the parameters are good. Usually clamped fins are a symptom of something else which I think would be the bad water conditions and stress. How far are you along in that cycle, if you aren't anywhere near finished I would just do a water change put him in the 5 gallon and proceed to do a fish-in cycle with some sort of bacterial additive. This is because it's easier to keep your water stable in a 5 gallon and will probably cause your betta less stress in the long term. Is he swimming well?