What does it mean if the vagina is too tight while i'm penetrating on her during sexual intercourse ? and her vagina still won't get loose ?!

Not loose, you lose: The vagina has a muscle around it that can prevent entry of anything from getting inside(pubococcygeus) by contracting uncontrollably.(vaginismus) Additionally, there may be a thin membrane(hymen) that is also "guarding" the entrance. A MD can solve the latter problem, but the former may require a therapist/psychologist for resolution. As a visiting "guest" you have to have permission for entry.