Just power up your eggy’s (he will probably remain on of the best grass attacker in the next cuple of gens) and try to find another high lvl double grass Pokemon.
I succeeded with 20 seconds left, my lineup was 1 lvl 39 exeggutor (BS-SB), 1 lvl 35 exeggutor (BS-SB), a lvl 29 RL/SB-Vileplume, and a lvl 39 C/DP Machamp.