Temperature/Heater Issues

[Klizzahrd]

I recently bought my 2nd betta and I've been having MAJOR issues keeping the temp at a constant 78. I had a 5 gal but the dorm RA had a fit so I had to recently downsize to a 2.5 gal -.-

The type of heater I have is a Tetra Submersible Heater for 2-15 gal tanks. It's one of those that shuts on/off so it isn't running all the time. When I had a 5 gallon this heater was GREAT and the kept the temp at around 78. With the 2.5 gal it fluctuates between 74 and 81 now.

so my question is:
Should I just take the heater out and let the temp stay around 62 all the time, or should I keep the heater in and let it fluctuate? Which is the worse of the 2 evils- water that is way too cold or water that changes 10 degrees in a day? I can switch back to my 5 gal in 2 months but I want to minimize the stress till then.

PS. It's a dorm. I can't turn the temp up it's stuck at 62.
And if anybody knows a heater that actually works in a 2.5 gal, pls lemme know.

[MyRainbowBettaFish]

the cold is worse...way worse..

maybe yo could get one of those reptile heating pads and wrap it around the tank?