"I'm an opened person" is wrong. "I'm an open person" means "I'm direct. I don't hide my feelings. I don't act or put on a mask. You always see the 'real me.'" "I'm an open-minded person" means "I'm willing to consider ideas that are new to me. I might change my mind." "Open" is one of those words... according to one online dictionary it has twenty-two meanings as an adjective, ten as a transitive verb, eight as an intransitive verb, and five as a noun... forty-five in all, not counting phrasal verbs! In this case, "open" is being used as an adjective. I am sorry to say that "I am an opened person" sounds very strange indeed. It sounds as a surgeon is operating on you!

I'm an open-minded person

"A" is used before a consonant and "an" is used before a vowel. Examples: "That's an apple." "That's a motorcycle." This rule is followed even in the past tense "That was an accident." When you talk about yourself and use "am" you are stating that you currently are a _______ person. If you wish to talk about what you used to be you would say "I was an open person." Or "I used to be an open person." The verb you would change is "am" not "open".

"I'm an open person" is correct! Example: Be an open person and keep up open communication with people you care about.

"I'm an open person" would be correct in this case. This is because you are talking about yourself in present tense. However, even if you were talking in past tense it would still be open instead of opened. "I was an open person."