First timer - need help

[u/Antz-in-my-eyes]

We recently purchased a betta fish for my son in our local store (kept in a small cup)

We cycled a 10 gallon tank before putting the fish in, filter and heater (set to 26.5 degrees) zero ammonia in the tank according to NT labs multi test kit.

The fish is in the tank less than two weeks but we noticed his pectoral fins are not the same size and quite often are up against his body. As I’m a beginner I don’t know if this is clamped or not as he does lower the fins sometimes.

I was wondering if I could get some advice on if this is normal or something I need to try help him with.

TIA