PRACTICE.
I am very cross-eyed dominant, and see two front and rear sights if I try to shoot with both eyes open, like you. It was awkward at first using the tape on my lens, but now during dryfire, I can take the tape off and switch dominance between eyes if I focus hard enough. I'm not comfortable enough to shoot a match without the tape, but I feel like I can get there after more and more practice with and without the tape.