Instead of trying to start Excel with the file, start just the file:
"C:\Project4\MonthlyTracking.xlsx"
This will open excel, if it is not running with that file, It will open the file within a running excel, and it will give you an error, if it is already open - which you can use:
"C:\Project4\MonthlyTracking.xlsx" 2>nul
if errorlevel neq 0 echo file already opened