When creating or editing the template, I didn't have the option to assign a signature field to myself (i.e., the sender/pre-filler). However, after receiving your response, I updated the template to reassign all of the non-prefill fields to Participant 2 (they were previously assigned to Participant 1). I added a signature field for myself & assigned it to Participant 1. I did not reassign any of the pre-fill fields. As suggested, I added my email address as the first receipient, and I was able to complete the fields that were assigned to pre-fill and also sign the field that was assigned to Participant 1. Participant 2 was able to sign as expected.
Thank you for the response & solution!