They are not both correct. ... The word "just" always comes after the word "have".
They are both correct / They both are correct.
The normal neutral placement is between 'have' and the lexical verb but there is some freedom for placing 'just' elsewhere.
You can insert other words such as recently, never, probably, always, etc to modify the phrase, but they always come after the "have"
I have never seen a penguin.
I have probably failed my examinations.
I have always told the truth
I have recently bought a car.
I have usually received the goods the day after I ordered them.
"I just have received the goods" is non standard. Is it the sort of error that non-native-speaking learners make.
If you wish to convey the idea of a shortfall you might say
"I asked for ten bottles but just got eight".
Again, the above represent the normal neutral placement. But,
I never have seen a penguin.
I have seen a penguin never.
Never have I seen a penguin.
Probably, I have failed my examinations.
I probably have failed my examinations.
I have failed my examinations, probably.
I always have told the truth.
Always, I have told the truth.
I have told the truth, always.
I recently have bought a car.
Recently, I have bought a car.
I have bought a car recently.