Regaining...

Look at fresh/frozen vegetables and beans at Aldi if you have one. Those are cheap and healthy, and if you have to eat canned food toss a bag of frozen veg in the microwave to go with it. While canned food is not super healthy it can work out, I eat canned tuna in water a lot because it isn't the worst thing in the world for you and its cheap. Also buying salads in their natural form, aka romaine, carrots, and tomatoes makes eating healthier cheaper too. My favorite desert is the frozen triple berry blend, its low in calories and sugar but pretty much any berry will do you from blueberries to strawberries they are all pretty healthy, just make sure there is no sugar added to them. Heck its not the best but even the dollar menu burgers from Mcdonalds can work out if you have a bunch of vegetables with them when you get home and ditch the top bun.

I wonder whether the bloating is because the canned foods you've chosen are high in sodium, and you're not getting the roughage you need with vegetables. One cheap meal is scrambled eggs with some cheddar cheese grated on top. You can add in some steamed broccoli, which is filling and gets you some of that much-needed roughage and green vegetable benefits. Bananas are inexpensive, as are some varieties of apples. Whole grain cereals, oatmeal and potatoes are possible ways to get you a more varied diet. I can't tell whether you're doing all your food prep in a microwave, but a baked or microwaved potato isn't too hard or time-consuming to prepare. It sounds like the underlying issue for you is food insecurity because your budget is stretched to the max. At the food bank I've volunteered at, they have canned foods, breads and fresh vegetables available. You would not be the only college student making use of this community resource, and I encourage you to check into it.

10 lb gain should be a wake up call but it is not devastating. How is an 8 lb gain ok but a 10 lb gain is devastating? It's mostly "in your head" so try to get a healthier perspective on the situation.
To gain 10 lbs in 2 years means you were overating about 200 calories per day. It's not hard to cut out a snack or drink each day to get back in a healthy range, especially if you're on a tight budget. Good point upthread that at least half of this, perhaps all of it, likely is water gain due to high sodium foods.