How to make a CCl3F Fluorine NMR standard?
You need the concentration of your reference peak to be the same order of magnitude as your solute. Accuracy of your integration depends on something called dynamic range, which refers to the relative intensities of the peaks being integrated. The greater the dynamic range; the greater the difference in peak intensities, the bigger the error. 

You might want consider that for most medium-high field NMR applications, CDCl3 is used with TMS at concentrations of about 0.03%v/v. Low field and bench top applications use TMS at 0.5-1%v/v concentration.