Hello Peagoimue38
Welcome to the SBB Community.
I am afraid, this is not possible, since there is not any proof of non-use.
And there is more: the total amount due would have been a new ticket plus CHF 90 surcharge, because you were travelling without a valid ticket.
The ticket inspector apparently removed the surcharge CHF 90 in your favour and you therefore beneffitted from extra goodwill, which is normally not granted as the conditions to use Supersaver class upgrades are transparently displayed upon purchase.

Thus, the Supersaver class upgrade is on your expense.
Kind regards,
Roland