big HONKING birds
9:25 is, at best, a mediocre collegiate 3k time. 2:20 is a very good sub-elite time, a minute off of an OTQ.
175 HR means you probably could've pushed harder. In no way does that effort translate anywhere close to 2:20 though.
I get that some people need to set unrealistic goals to stay motivated, but if you train and try to race like a 2:20 marathoner right now you will blow up.
There's nothing wrong with having that as a longer term goal, but don't delude yourself for the short term.
For goodness sakes it's your first marathon. Run it without crashing and burning then report back.