David Peterson’s return to the rotation went about as well as the rest of this cursed Mets season. The left-hander allowed seven runs — all earned — in just 3 ²/₃ innings in Wednesday’s 14-2 loss to the Nationals at Citi Field. And because the state of their pitching staff is so bad, Peterson will almost certainly remain either in the rotation or used behind an opener the next time through the rotation. “He’s a big part of this team,’’ Carlos Mendoza said. Peterson said his issues stemmed from falling behind in counts. He also walked three batters, but insisted he could right himself. “I’ve done it before,’’ Peterson said. “And I believe in myself and I know I have the stuff to do it.” Mendoza also expressed belief that Peterson has the ability to be effective. “We’ve seen flashes of it,’’ Mendoza said. “He’s got more than enough to compete in the strike zone.” David Peterson wears a dejected expression during the fourth inning of the Mets’ 14-2 loss to the Nationals on April 29, 2026 at Citi Field.…