Gaining weight is just down to more calories consumed than burned. It doesn't matter whether it is 'healthy' food or unhealthy.
On the other hand, not eating a healthy balanced diet will lead to bad skin, spots, lank hair, weak nails and all sorts of other issues. You don't need a lot of space to exercise- grab a couple of cans of beans for arm exercises, squats are done on the spot, a t towel held taut while doing vertical rowing/arm raises is very effective. Stop looking for excuses to eat poorly and start thinking of creative ways to eat well and move more.