That's not a nested ticket. It's completely legit as far as the airline is concerned.

Nesting is when you try to use 2 tickets to avoid conditions like minimum stay. So if you bought a YYZ-SDQ trip with 14 day minimum stay and bought a SDQ-YYZ ticket to retun to YYZ after only 3 days from the outbound leg of the 1st ticket, that would be a nested ticket.

Since you are continuing on to a 3rd destination, it's okay.