SSD lost space

Hi there,

I bought a secondhand macbook with a 500GB SSD installed a few months back, but only the other day I noticed something bizarre. While under the storage tab of "about this mac" it says 500GB Flash storage under the drive pictogram, the bar only says 350GB. Terminal "diskutil list" says the following:

Last login: Fri Nov 29 05:34:40 on ttys000

Matthijss-MacBook-Pro:~ °myname° diskutil list

/dev/disk0 (internal, physical):

   #:             TYPE NAME           SIZE     IDENTIFIER

   0:    GUID_partition_scheme             *500.3 GB   disk0

   1:             EFI EFI            209.7 MB   disk0s1

   2:          Apple_APFS Container disk1      351.0 GB   disk0s2

/dev/disk1 (synthesized):

   #:             TYPE NAME           SIZE     IDENTIFIER

   0:    APFS Container Scheme -            +351.0 GB   disk1

                  Physical Store disk0s2

   1:         APFS Volume MacBook          11.9 GB   disk1s1

   2:         APFS Volume Preboot          79.0 MB   disk1s2

   3:         APFS Volume Recovery         1.0 GB    disk1s3

   4:         APFS Volume VM            1.1 GB    disk1s4

So the 500Gb has an asterisk, but doesn't get specified. The second time is says +351GB, which means it is more than 350GB, but also not specified where the other 149GB went... I would really like to 'recover' the 149GB, as I needed that much space to start with...

Anyone here who knows this problem or can help?

Massive thanks in advance!

Cheers,

Matthijs