Issues with RF transmitter project
You have at least two "sources" for the "discrepancies."  The first is the variability (tolerance) of the components, and the second is "parasitic" capacitance. 
I recommend adding a "trimmer" so that you can adjust the frequency of the 7555,  Also, it seems you are overloading the crystal oscillator.  You can try a smaller coupling capacitor and/or more amplification.