Hi Jessica,
Ah OK, sorry, didn't realise that.
If only you could delete the erroneously completed form(just the form, not the record), then maybe you'd be able to compose the invite from there again.
But I took a look at a similarly completed uneditable form in one of my trials and there's no delete option.
So maybe the only option is to do what you already did and grab the link from the survey invitation log and manually send an email. (or click on the envelope to get the text of the sent invite).