I accidentally looked into the green light that was scanning paper in a copy machine when opening the lid to check for paper for a 3 seconds? any risk

Unlikely: If you are having issues with eye sight you need to get it checked, otherwise it is unlikely that it would cause problems

Scanner green light: http://www.light-sources.com/solutions/specialty-fluorescent/applications/copiers-and-scanners/ It appears the light source, is florescent so do not worry. If burning , pain, foreign body sensation , decreased vision follow up with Doc /urgent care or ER.