Hello,

Don't worry about the scanners. If you have darkened the bubble more than needed it's ok, it scans the omr sheets. You won't get any negative marking over there.

In such central exams, the scanners flash the light against the omr and try to find the contrasting differences available. Well as the light flashes over the sheet the lighter shades like erased pencil marks and all are same and won't be contrast. See that's why dark bubbles are allowed and if you had put a bit more dark it's ok.

Hope this helped. Thank you