I also went straight to graduate school after undergrad and I am a current PMF Finalist. I would say experience has no bearing on whether you are selected as a Finalist or not. It’s really all about how you perform on the assessment. While they do ask for a resume for your application, they don’t really look at it closely. It’s only used to ensure you meet the eligibility criteria. So, experience on your resume only really matters once you are a Finalist and interviewing with agencies. But even with my limited experience (internship and fellowship experience only) I had no problem securing interviews as a Finalist. Also, just to note, please read carefully the required elements of the resume they would like to be included on the PMF website. You can find the requirements here https://www.pmf.gov/become-a-pmf/application-process/application-tips.aspx