I think if you are new and it is petstore fish it isn't very easy to keep them alive, well let's face it, conditions in the store suck, after a while their immune system goes down so you need to be careful. I have "killed" 5, in less than a year. Out of all those at least 3 were from the first hours/days which is when most fish will die, after that it is smooth sailing, sometimes lol. One got a malfunctioned heater and the other had dropsy in which I literally had to put him to sleep.
Just remember you start somewhere. Also those bettas died knowing someone loved them, so I think it is better to accidentally kill 8 bettas and house them properly than let's say leave them in the cup. Honestly most people won't buy them and give them proper homes, they usually just fight them :(
Also identify what you are doing wrong each time. You can't succeed without failing after all.
15 Gallon NPT
1g no tech bowl in the making