My flight simulator X landings are having problem.?

the problem is that whenever i am 500 ft above ground level then i freeze my altitude until i reach a few meters fro the runway but something happens before that something starts to sound. it says "pull up, pull up too low gear" and then in few seconds it starts to increase the throttle automatically and i will skid off the runway because of the speed. So if someone knows the solution please tell me.