i found a glitch, on lvl 15 near the end, it lets you pull the orange 1 down and you can see it going through the purple. the orange then comes all the way out and through the purple. :)
If something is rotationallt symetrical it means that it can be rotated by the central point (in this case the coloured circles) by 180 degrees and fit perfectly in the shape still. For example, I is rotationally symmetrical but T is not.