How to COMPLETELY delete big sur installer

Yesterday I tried to download Big Sur since it said it only needed 12gb and I had around 22-24 left.

So then when it finished downloading and I tried to install in my mac it said that it needed at 16gb I think (and I already lost around 12gb downloading the installer so I only have around 9gb now) so I tried to delete the installer, moved it to the trash and deleted it permanently. But when I saw my storage again it was like I haven't done anything and I still only have 9gb left of free space and I don't know how to properly delete the installer or whatever left to delete.

My mac is using macOS catalina 10.15.7