Need advice on grad role

Context:
Currently looking for a grad role in marketing. I recently interviewed for what was advertised as a "Graduate Marketing" role and built great rapport with the marketing manager and the interview went great.

Issue:
During the interview, the reality of the role turned out to be very different from a traditional graduate program. It is a 12-month contract covering someone's maternity leave, with only a loose possibility of extension. And the marketing department is small, just the marketing manager and one other person.

The manager told me that "success means working independently." He explained that I will be expected to create, run, and manage live digital ads. They will actively track and compare the performance metrics of my ads against theirs to decide what to run. Because he sounded like he needs an immediate replacement, i am worried there will be little to no structured training or mentorship.

Concerns:
While I know getting my first professional corporate role on my resume is a great first step, I am terrified of the "sink or swim" pressure. I am worried about imposter syndrome, and the risk of underperforming and being let go during probation because they expect an experienced mid-level marketer on a graduate salary.

Does anyone have any experience with a similar situation?

Should I walk away and look for a true graduate role that offers proper mentorship, or is any experience better than no experience right now?