When you have limited space and funds-you can still successfully keep a betta-provided that you are willing to make the needed water changes.
Although-a 2+gallon filtered, heated tank is best and can give you some wiggle room so-to-speak....when life happens.......you can still successfully keep a happy thriving Betta Splendens in smaller volumes of water in my opinion/experience.
Using live stem type and/or floating plants can also help in maintaining water quality and giving you that all needed wiggle room when life happens.........
In 1-2g-unfiltered containers with one adult Betta with or without live plants, a few hiding places and something in the tank that goes all the way to the top-like a plant leaf (real or silk)-by making 2-3 times a week 50% water changes and 1-weekly 100% water change should keep the water quality at levels safe for the Betta-provided that you don't over feed and you remove any uneaten food after feeding.
Keep the water temp within a few degrees from new and old water with water changes to prevent temp related problems and use a good dechlorinator with any water added to the fish if you are on city water supply-you want to find a dechlorinator that covers-chlorine, chloramines and heavy metals. Run the water through the tap for at least 1 minute to clear the line of most of the metals that can pool before use with the Betta-especially if your dorm is in an old building.
Make a 50-100% water change anytime you see any behavior change or odd behavior even if you just did a water change earlier in the day....the first thing you want to rule out is the environment...sometimes it can be as simple as not enough dechlorinator or something on your hands.
Water temp is a big issues in the smaller tanks, however, you can get the small 7.5w-10w heaters and safely heat the tank-keeping the water in the 76-80F range
Ideally-larger is better, but often we can't provide that for what ever reason and that shouldn't keep/stop a person from enjoying this hobby and keeping a Betta..........