There will be many other candidates that have multiple varsity letters and other athletic accomplishments (All State/All Conference/ etc), so it won't be a distinguishing characteristic to have a single varsity letter from a season that hasn't even ended.
However, the SA is going to evaluate your entire application and compare it to your peers, so it is unlikely that a single data point will make or break the candidate. In short, they are going to look to see the entire package you submitted and see how that stands with other candidates.
Did you excel on the CFA? Do you play club sports? Do you live in an area that provides little opportunity for high school sports? Do you work 40 hours a week supporting your family? Did you max the ACT/SAT? Did you play high school sports but just never made the varsity (some schools are huge and making the high school team is very difficult, I went to a small school and making a team and lettering was easy)
At this point, your package is what it is. If you have a nomination - you are still in the game.
They have allowed me to do Track this year after some persuasion. Yes, I am still enlisting but I am still curious about the process since a friend of mine is in a very similar situation to me and he HAS applied and received a nomination but lacks a varsity sport.
Few homeschoolers or kids who go to small high schools (our local high school will graduate only 29 students this year) have any opportunity to earn varsity letters and for some, even finding club sports may present difficulty.
Keep practicing for the CFA, in order.
Also, if you are not set on enlistment, maybe take a gap year at local U where you can participate in sports at a higher level?