Is your ECA from WES? My WES ECA (and of my two cousins') nowhere says that it's not an official copy.
However, it says "This WES ECA report is intended for use in connection with a IRCC immigration application. IRCC will verify the report against an electronic copy from WES. Your WES ECA report will be voided and not accepted by IRCC if it is found to be altered or modified in any way.", which is different from saying whether it's an official copy or not.
If you are applying to enter into the EE pool, you do not need to submit your copy of ECA, you only need the reference number and date of generation of ECA. In fact, you are not asked to upload the ECA certificate anywhere in your entire application, even, post ITA, they verify your ECA through the reference number you give them.
Anyway, to order a duplicate one, you need to log into WES, under completed section, there will be two options "Order Duplicate" and "Download". Click on "Order Duplicate" and proceed, make sure that you add yourself as a recipient.