Need help in, 2.45 GHz Rectangular Patch Antenna, HFSS design

I have a uni project, and it's about designing a patch antenna which have a Fr=2.45GHz and the return loss must be between -15db and -33db.
Given:
h=0.6mm ξ=9.8 fr=2.45GHz
Probe Fed
I used formulas and calculated the patch dimension and the substrate dimension too!
I just managed to get 2.44GHz and 2.46GHz results, but not the 2.45GHz, i tried to change the position of the coax and its dimension but nothing helped...

NEED HELP ASAP pls