Scanning of a coin isn't so very simple. You should do the following:
1.Use a sufficiently small calibration corner.
2.Set the resolution of your camera to its highest value. Fill its image area in this way: 1/3 of the width with the coin and 2 x 1/3 with the calibration sheets, respectively left and right of the coin.
3.Coat the surface of the coin to make it matt:viewtopic.php?f=2&t=1283
4.You can move the laser by hand, better is to tilt it by a very slowly motor. Maybe by a kitchen timer:viewtopic.php?p=2016#p2016
5.Better is to move the laser line one time very slowly over the coin (and the corner) than multiple times and faster.
6.Use a big intersetion angle, best about 40°:viewtopic.php?f=2&t=3117&p=17498&hilit
7.Focus camera and laser sharp to the coin, not to the calibration corner walls behind the coin.
8. Disable all automatic functions of the camera, e.g. autofocus.
The green fosusable laser is well suited:viewtopic.php?p=1393#p1393
A blue laser is not much better, maybe a bit.
PS. Can you post a photo of your set-up? Have I forgotten something? Maybe if I have seen your set-up.