Hey BettaFishRule! Welcome :)
I also have a 2gal setup, and it's definitely very important to get a heater. I got a very good adjustable one (which is very important, because Bettas should be at least at 78* but some like it warmer) from PetSmart for just $12. It just sticks to the back of the tank and no problems :)
You should also get a thermometer so you can tell what temperature your tank is at. Chances are, that once you heat up the water and give Aragon some time to adjust, he'll be doing just fine!
Also, Bettas like pellet food much more than flakes, so you might want to get ahold of some of that. From what I've heard, many Bettas (including my own) LOVE something to hide/play in--just make sure that any openings are at least the size of your thumb.
It may take him a little bit of time to adjust, so don't worry just yet :)