mobile

I had the optimus g3 rom(had 32 gb storage) on my phone but flashed back to stock since i had to send it in for repairs under warranty, i flashed stock rom and my phone showed as 16 gb with around 10 avalible in storage but if i went into hardware information this stayed the same even after i downloaded multiple stock roms just to make sure i hadn't downloaded the 16gb version (i even tried using lg mobile support tool).I got it back today and installed the offical 5.0.2 with the flash tool and in storage it show it is the 32 gb version but shows system data is using up 20.5gb.Any ideas on how to fix this and get my 32gb back?