I've combined 3 embroidery files by copy/paste. When I print it out the center point of the embroidery design is not in the center of the embroidery design. Does anyone know what I need to do to get the center point in the right place?

The center point will be calculated for the left and right top to bottom and put in the center, if you want to over right the choose center location. Depending on  your version you get goto set start/stop either in the edit tab , or on Version 11 got the Layout tab .. and choose To design - Align centered on Design.. You should get a page at the top, it should indicate one location. Choose this, and then choose user defined, then click ok , this will allow you to LEFT click on your embroidery design and center location.This would be your choosen start /stop point that your machine will use to trace the embroidery design with.

I also want to do embroidery for my wedding by using software. So, I have a software in which I did the same steps which you said above but its not working can you please suggest some new. So, I can design my plus size wedding dress. I want some suggestion on flowers to design. How to put color by a thread through a software.