Semester ended early May for me, then i went on vacation for a month, came back, started working, and JUST went back to the gym after 2 months. I feel like $h!@, moreover Ive gained somewhat of a belly and my chest has gotten kind of flabby, been eating out a lot

Going back to college in 1 month, already joined the gym, but what should I do? Extreme cardio? I dont want to lose muscle either, I want to get back in shape. Whats the best suggestions for this next month?
anything is appreciated