Your code includes this comment:
/* sample for digital weight scale of hx711
* library design: Weihong Guan (@aguegu)
* library host on
*https://github.com/aguegu/ardulibs/tree/3cdb78f3727d9682f7fd22156604fc1e4edd75d1/hx711
*https://github.com/aguegu/ardulibs/tree/master/hx711
*go here for directions on how to use
*/
Did you go there and follow ALL of the directions on how to use it? Judging from your code, you did not do the entire process. The weight you use for calibration should be near the full scale value (load cell capacity).
What does your voltmeter read across A+ and A- at zero load and at full load?
PS: also, you did not include the link to your load cell spec sheet. Please do. And show your wiring.