Reduce reactance of planar tapered slot Vivaldi Antenna

I am desiging a tapered slot Vivaldi antenna using a double-sided Marchand balun. I would like to match the input impedance to 50 ohms. I am using FEKO to simulate the design. I am having issues with obtaining the 50 ohm match and am getting a high reactance value.

Can anyone please suggest what I can try to decrease the reactance of my antenna?