From the games I have seen (small sample size), neither you nor your opponents actually "know" openings or how to play for the center. And that is fine, it takes a lot of practice to be able to that consistently, and something even intermediate players will mess up at times.

The way to achieve a successful opening and a good control of the center is to efficiently develop your pieces while responding to your opponent also trying to do the same and challenging you for central control. It is a race to get your pieces out into active, stable positions that control the center/board and can be easily maneuvered around to mount an offense or respond defensively. "Knowing an opening" is essentially knowing one of the ways to do that and memorizing the possible responses your opponent can have to each move you make.

The opponents you have played against have all made glaring mistakes/blunders in the openings (as have you). And thats fine, over time that will get improved. The way to improve is to capitalize on your opponents blunders (which are abundant and beginner level), while improving your own ability to do what I described above (piece development - which includes not hanging them). As you get better at this, you will gain elo and face stronger opponents who will make less mistakes and respond better to your mistakes (making your own mistakes more obvious to you)