Hello, I'm a newbie to using vacuum forming. In the image attached, you can see there are 2 holes in the plastic. This pic is my 3rd attempt, my 2nd attempt also had holes. However, my 1st attempt did not have holes. I am not sure what I did different. I'm guess it might be with the duration of heating the plastic before hand. Might anyone be familiar with how to solve my problem? Thanks!!!