about LTC3862 FB(feedback) voltage

i have designed a LTC3862 solution, designed output voltage is 107V/1.5A , and the circuit is same as LTC3862 datasheet parts 107V out circuit. but when measure the output points, it has not 107V , and i change the feedback resistor is not work , the feedback voltage is 0.8V more or less.  the output connected a electricLoad , has 90 ohm, when i tune the electric load to 100 ohm, the output voltage changed to bigger, the Feedback voltage changed to bigger also. i have measured the ITH pin voltage is 2.7V . could anybody teach me where is going wrong ?  please teach me.