More bytes required to fit sector
 

I have an image which is 38434551744 bytes in size when i tried copying data into it from another image which had 7506937 sectors the copying failed saying no space left on device So i increased the file size to 3843552256 bytes and i was able to copy over the data now my question is why did it require that extra sector of 512 bytes since 7506937*512=38434551744 which should have fit in those sectors. Is it because of the MBR the first 512 bytes or I am doing something wrong.
So even if i create a file of size 38434551744 bytes I cant have 7506937 sectors? Also to mention is i am using fdisk for partitioning.

window file system default size on disk is one sector i.e. 512 and for extN/linux file system default size on disk is 4k i.e. 8 sectors