dspic Timer1 Interrupts Occuring Twice as Slow
Your code is right, you are actually toggling  the pin at 200Hz... That means its frequency is 100Hz.

The period you are setting in the timer is the distance between a rising edge and a falling edge, and vice versa, so the wave period will be twice the timer period because the wave period is defined as the distance between two rising (or falling) edges.

Go with the value that works and you will be fine.