Stop the world and let me off

I’m working on a project in my job, where I feel very underprepared as they asked me to fill in for someone a last-minute and I had no training. I know that even though know very little about the project, I’m great at solving problems and figuring things out so intellectually speaking I know I will be all right. The issue is that my brain is offering the thought “I’d like to stop the time, sit down and plan for all this” this seems nice to think about but it feels awful. This comes from scarcity, like I had no time at all. And when I have free time and I can actually plan, my brain tells me, don’t plan, it’s a waste of time, better get to work on some issues now and put out some fires. And if I do not action on that, and watch TV I feel so guilty. Please help!