STM32F413ZG Program Size - code, RO-data,RW-data,ZI-data


I use STM32F413ZG that has 1.5M Bytes flash and 320K bytes RAM. When I use Keil uvsion5 to finish Compile, I get the below information 

Program Size: Code=902,730 RO-data=594,458 RW-data=4,380 ZI-data=323,084

According to document said:

ROM(Flash)=Code + RO-data= 902,730 + 594,458 =1, 497,188, is very close to 1.5M flash?

RAM=ZI + RW = 323,084 + 4,380 =327,464 , is larger than 320K RAM ? 

I confused why the RAM larger than 320k,  my program still can run correctly?

And the flash close to 1.5M , that means I cannot add ne function in the future?

Is there any way I can reduce the RAM and ROM usage?

Thank you so much !

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