1. This shop was just opened 3 days ago.
2. This shop has just been opened 3 days ago.
1. Do they have the same meaning?
2. Are they grammatically correct?
You'll hear them both but I don't really like either of them. I don't see the need for "just" along with the actual timescale.
This shop just opened.
This shop opened three days ago.
Note that as far as I'm concerned, "just" would refer to a time much more recently than three days ago. "This shop just opened" would mean to me "This shop opened its doors about half an hour ago."
"This shop opened for business [just] recently" might mean it had opened in the last few days.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.