Since both players try to "control the center" what often ends up happening is either each player controls 2, or maybe one player has 3 and one player has 1.
It shouldn't be too hard to control 1. For example if you put a pawn on d5 as black, then e6, c6, Nf6 and the queen (on her starting square) will all protect d5... and if you're able to keep a pawn on d5 then your opponent wont be able to put a piece on e4, so that's basically 2 squares.
Sure they could attack your center with a pawn (e4 or c4) but hopefully you can attack too) e5 or c5) and things will stay even.
Anyway, it's hard to give advice without seeing a game.
I've complained about my atrocious skill in multiple circles of mine and the most common tip they've given me is "control the center." As in "get pieces on those four squares at the center of the board."
Okay... but my opponent is also trying to do it, too. And when I try to take territory in the center, I'm losing. My pieces are either hanging or sparsely defended. I'm never in a good defensive position while trying to "control the center." What am I supposed to do?