Then it sounds like you don't have a choice. Decline it so that you have a chance to get an ITA (although it might be too late to be included in the draw even if you're above the cutoff). It;s a tough position to be in.
Your other option is to try and collect documentation that proves you did your best to get the PCC in time, and then later send the PCC via webform. Personally I'd be quite uncomfortable doing this, because it's IRCC you're dealing with. Any opportunity to reject, they will take it.
I hate to say it but in your position I'd probably decline and hope to get another ITA in the next draw. Good luck, hope there are no issues.
I was unable to provide PCC myself and sent them a letter (LOE) explaining it.
They gave me 2 additional months to provide the document.
It's risky to decline : we're not certain of the next draws.