First, the "lerp" doesn't work on triggers.
Second, the use of lerp is to progressively change a to b every tick or delta-time(dt) using (c).
Syntax: lerp(a, b, c) every tick or lerp(a, b, c * dt) for optimization.
If that is your goal then, you are on the right track.
If you want the mouse for lerp then I suggest you use a variable or boolean.
global number variable (Switch = 0);
global number variable (A = 0);
global number variable (B = 0);
global number variable (C = 0);
*global variable Switch > 1
->global variable Switch set to 0
*On Mouse click.
->Add 1 to global variable Switch.
*global variable Switch = 1
->Set scroll to x (lerp(A, B, C * dt).
Hope that helps.
BTW, that event is for scrolling x.