Help!! Fish rot or not?

I have gotten my first betta fish last week and I have realized yesterday that he (Hanzo) has holes and dots on his fins. I initially thought it might've been because of a rough decoration but I'm starting to worry it might be fin rot :/
Looking back at old pictures he's had the black spots on his fins since I first got him but the holes are new.
He is currently kept in a 3 gallon tank, heated and filtered.
Thanks for your help
(In the picture below he was flaring at a mirror)

 

Doesn't look like fin rot. It could be because of decor but it could also be poor water quality. Your profile says you don't know about the nitrogen cycle so I'm willing to bet its ammonia. Read up on it and read a few tutorials on how to do a fish-in cycle.

 

I have gotten my first betta fish last week and I have realized yesterday that he (Hanzo) has holes and dots on his fins. I initially thought it might've been because of a rough decoration but I'm starting to worry it might be fin rot :/
Looking back at old pictures he's had the black spots on his fins since I first got him but the holes are new.
He is currently kept in a 3 gallon tank, heated and filtered.
Thanks for your help
(In the picture below he was flaring at a mirror)

do a water change I'm sure that its bc of an ammonia spike. putting it as basic as possible, fish pee and poop, we will call this ammonia. so ammonia is toxic to fish and can kill them, that's why when u just put a fish in a bowl of water without being cycled its likely they will die. so as ammonia builds up in ur tank bacteria grows to break it down to less toxic stuff. when that bacteria is present ur tank is considered cycled and is able to break down all of the fish pee and poop to prevent poisoning ur fish

 

do a water change I'm sure that its bc of an ammonia spike. putting it as basic as possible, fish pee and poop, we will call this ammonia. so ammonia is toxic to fish and can kill them, that's why when u just put a fish in a bowl of water without being cycled its likely they will die. so as ammonia builds up in ur tank bacteria grows to break it down to less toxic stuff. when that bacteria is present ur tank is considered cycled and is able to break down all of the fish pee and poop to prevent poisoning ur fish

if I m wrong in any of this please correct me if I'm wrong. how big is the tank? and r his gills red

 

Thank you for the replies, I decided to take out the decoration that I thought might be too rough and I took a look at my water conditioner. Turns out it does not help with ammonia or nitrite concentrations. So I will go buy another and change my water more often than once a week. Hopefully this helps him ><

 

if I m wrong in any of this please correct me if I'm wrong. how big is the tank? and r his gills red

His gills do seem to be red (I can only see them when he flares at his reflection in a mirror though) and he is in a 3 gallon tank, heated and filtered.
sorry for the blurry picture its the best I could get

 

get fin rot meds and give him that u can get it at like any local fish store I believe