I am assuming that the buckle is up and not down. Perhaps something heavy and flat and spanning well beyond the buckle would, but to get it perfectly flat maybe not. If it is in your driveway, you must add a dehumidifier or at least keep the vents open to allow moisture to escape as the temps rise and fall. Wood and pressed board does absorb moisture from the air. With moisture it will bend even under its own weight. You might see if you can add some angled aluminum with construction adhesive to stiffen and support it from the bottom. I would hope the the counter top is mounted on a sub surface. If not, it will bend over time no matter what.
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