there is "not enough memory" in excell for me to save a new document

i have a 10.9.2

there is currently 51.8MG in excell

the file i am working on is 2.9MG.

but when i go to create a new sheet with a pivot table a message comes up saying "not enough memory"

i went to try and increase the memory and found that there is plenty of memory in excell

so why?