If it was shave ready from SRD, it was definitely sharp. Did you try stropping before using it the first time? If so, you may have rolled the edge.

If not, hopefully it's just technique. Maintaining a ~30 degree angle and using no pressure are paramount. I suspect you would have some of the technique down since you're using a disposable straight now. However, a "real" straight has a much different feel than a machine sharpened blade. It may just take a little while to get used to it.

If in doubt, contact SRD. They are good guys and will help sort it out.