I did my first 3d model and ran slicr, and got that error, 'not mannifold'. I looked it up and .... it's beyond me. I ran a repair program (azuretoolbox) and it not only couldn't fix it (it says it did), but when I load it, there's no image and it prints in 0 seconds (and does nothing). I used all separate lines in my model. What did I do wrong?