ActionScript 3.0 :: If Conditions Using Formula And Input Text?

Currently, we have an activity in class wherein we're supposed to resize a Movieclip to a specified size restricted to any value between 50 and 250% that will be entered in an input text field. If the value entered goes beyond 250 or below 50%, it's also supposed to show a warning that the entered value isn't valid. Also, when a value is entered in the textfield, supposedly, it can be entered either by using the ENTER key or by clicking the resize button.

I've already managed to resize the movie clip according to the amount specified but I think there's something wrong with the "If" condition in my resizeShape function, because it still accepts values above 250 and below 50%. Also, I don't know how to make it so that both pressing the ENTER key and clicking the resize button enters the value without repeating the whole resizeShape function.Here's what I've done so far:

ActionScript Code:
var input_txt:TextField=new TextField();
var warningBig:TextField=new TextField();
var warningSmall:TextField=new TextField();[code]...........