Can’t get official graduation date from self-paced, online high school. Will this stop my enlistment process until I graduate?

Hello all, I’m 17 years old, and I attend, the self-paced, online High School Penn Foster. My recruiter said that I would need an official letter from Penn Foster stating my official graduation date, to get the enlistment process really going. However, I called Penn Foster, and they said the best they can give me is an official letter stating that I’m enrolled, and will complete the program within 3 years of that enrollment date. Will that work the same way? I’m on track to graduate in February of 2020, but 3 years after my enrollment date is August of 2021. Everybody gets 3 years to complete the program, and most graduate before that. Will this stop my enlistment process? Or is there someway I can still be enlisted, even if Penn Foster can’t give me an official graduation date? Im worried I’ll have to wait 6 months to continue my enlistment, and the job I wanted just got over 100 openings. Sorry this is all over the place, if anything is unclear, do ask.