reveal text from the center outwards

I have a line of text that I want to reveal from the center out. I tried making 2 shape layers as masks each moving in opposite directions to reveal the text. I want to use the scale for the mask so it hides the side of the text I don’t want to see. However, there is drift in the scale even though I have unlinked the scale parameters. It is about 5% drift that reveals the side of the mask I don’t want to see as the correct side of the text appears. How do I do this?