first, pushing horizontal to the right will give a value from 0 to 1, and to the left, 0 to -1. you can round these numbers to work with solid variables, but axis values are .99999999 or .00000453 or something similar most of the time.
What I would do is check every frame to see if horizontal is more than .25 or .33(find a dead zone that works with your game) and if true, do your lean thing. not sure if youre playing with animation or raw, but do it then. if it falls below your dead zone, undo the lean.
if you wanna see what I mean about the .12345678, set up a gui text that displays the horizontal axis vale every frame(store the value into a float every frame, convert the float to string every frame, and update the gui with new string every frame I keep a "debugtext"(that's what I call it, not playmaker terms) around because they are useful for everything)