It should still be doable if you stick with it. I started during the Monotropasturum event and during the first few days, the same - I could only beat the Beginner maps. Later I managed the Intermediates, and managed to squeak through the E16-3 advanced map once (barely). I still got Monotropasturum with 2 dress blooms and 2 skill blooms. You just may not get a fully kitted out Lunaria.
Get a strong helper squad if you can - that should be able to get you through (although maybe not 3-medals) at least the intermediate and maybe the advanced maps as the event goes on.