I do not think you can cut such thick acrylic with such a low power laser. I have a laser cutter with 60W tube, and I'm doing fine. The cheapest cutters usually mount at least a 40W tube.
With a 2.5W laser, I do not think you can cut something thicker than a paper, those lasers are not made for cutting, you need much more power and that is only achieved with tube lasers, not with solid state lasers.