The only possible correct version of the sentences is:
'If it was meant to be, it would have happened already' - This is a hypothetical sentence, which means that it is not meant to be because it has not happened.
The sentence 'If it was meant to be, we would already have got married' is correct.
These sentences are both mixed conditionals, where the 'if' part talks in general about 'if it was meant to be', and the 'would' part talks about the past.
Other similar sentences are:
'If I wasn't so stupid [in general] I wouldn't have failed the test' [past]
'If she was interested [in general] she would have called by now [past]
Back to your sentences, if it is still possible that something is meant to be, then you can use this sentence:
'if it is meant to be, then it will happen' - This is first conditional to say that something is possible, it is possible that it is meant to be.
Hope this helps!