I am somewhat new to the hobby, I've flown a couple planes. Right now I'm building one from a kit, but after turning on the ESC it wasn't working correctly. When the throttle from the transmitter is at 100% the ESC thinks it's at 0%, and vice versa for when the Throttle is at 0%. I am probably being stupid, but I haven't found any way to fix this online.

I'm using the Skywalker 40A UBEC as my ESC, and the AT9S as my transmitter.

In your transmitter, reverse the throttle channel Should be a setting for this or on low price transmitters there is a switch.