Q: Free Space Disappear in internal drive

Hi y'all...
I have a weird situation and i will be happy if u could help me,
i had 2 big projects on my Macbook Pro ( (mid 2013) 15.4 Retina with 512SSD drive) for a long time and today i finish them and copy them for external HD to free up some space on my laptop, the projects both took like almost 350GB of my 512GB SSD so i had to delete them, after i delete this 2 folders and move them to trash bin and empty the trash bin i still don't see this empty space
in one hand the drive seems to be ok and show me that i have 383GB available but on the other hand i see that almost 300 GB been taken my Backup file (don't know where it come from or what it is) and  i can't find it on my drive and when i tried to copy new project to the laptop it says that there is not enough space for it (and the new project is  "only" 120GB)
how do i fix this plz ?

P.S: I add few screenshot to let u understand what i meant
Thank u very much
Amit