We usually recommend getting through as much of you can of the phase progression. In certain cases where an athlete has been riding regularly and has a good base, they can skip Base and move straight to Build. However, this is pretty rare since there’s a notable difference between a general aerobic base cultivated over lots of road miles, and the type of adaptations that can only occur with structured training.
In your case, I’d recommend making the most of your 10 weeks before your event by continuing along your training path and completing SSBLV2, then getting through as much as you can of the Sustained Power build phase next.
You can learn more about this here:
Plus, once you’ve done one race, there’s no way you won’t sign up for more! 
Let’s consider this first race for you as a B or C priority race, meaning that it shouldn’t interrupt your training as you work towards future (albeit undefined as of yet) goals. Best of luck!