Planning calculation

hello,
I think i don't understand very well how planning calculation is working on projeqtor.
For instance, i've got a project divided in some activities. The first activity was suppose to last for 3 days but when i allocate 3 days of work on that task i only get 68% of progress.
Plus it didn't reach 100% until i change the status of the activity from "in progress" to "done" and now the plannified date just change to the date i made the status change and now my project is planned to end later than i excpected.
I think i don't understand the calculation formula or i misunderstandthe tool.

thanks for helping.

I figured out another issue with planning calculation.
When i want to plan a project in the future for instance asked Start date : 01/01/2019 and asked end date : 31/12/2019 and an activities asked Start date : 01/01/2019,asked end Date : 31/07/2019.
Then when i look on the planning i can see progress bar between the right dates but when i add on my project validate Start and end date (let's say i validate 10 days later than the asked dates) planning calculation run and progress bar are put at the date of the day.

Am i doing something wrong?

thanks for helping