I'm away from my desk at the moment, so can't check your source file. It sounds like you need to turn off the 'resize text' setting in your text box. You may also find using an invisble shape, rather than a text box, gives you better control in these circumstances. Sounds like your text is too long/big for the text box.
But if your text doesn't resize, you run the risk of it spilling out of the display area. So I recommend testing your longest possible JS-generated output and sticking to a rough character count based on your font choice and font size.
That's what I did here with JS-generated text.
