Maybe not last, and it'd depend on the event.
At bigger events, for every blisteringly quick rider in a class there's often one or two that are properly slow. Less so at smaller ones.
Looking at times from the last year or so, and people I'd expect you to be beating (after a year or two of learning the hills), on average I reckon you'd be looking at around 15-17th of 22-25 in the open 750 class at a big event with a lot of entries. At a smaller event, yeah, you'd be fighting not to come last.
When I was starting out, I mostly used "am I beating Simon?" as the litmus test. It's important to have achievable goals.