Kind of strange function,
but the main thing you should change is to never use wait(10);
this waits 10 frames, and not a specific time, use the negative number like wait(-0.1); or so
for time in seconds. (is like sleep() function)

var fps_max=120; //limiting the framerate an fast computers

...

while(my)
{
my.x -= 3* time;
if (my.x < -3600)
{
my.y += 10*time_step;
if (my.tilt <= 15){
my.tilt += 5*time_step;
}
ent_create(bullet1,vector(my.x-20,my.y,my.z),move_bullet1);
wait(-1); //or another value, that is not framerate dependent
}
wait (1);
}