Hi Alex,
I presume you had a 2-year insurance contract when you first entered Canada, and a 2+ year passport validity as well. In that case, the BSO made a mistake by limiting your work permit to 6 months.
This falls into the
category #1 issue and you will need to send a paper application to the Edmonton IRCC office. Please note that you cannot submit your extension request online. This must be sent by mail.
You will need the IMM5710 form, a copy of your passport and work permit, and also a copy of the CBSA stamp, a proof of insurance and an explication letter. No fee is required since you are an IEC participant.
Hope this helps!