Girls-Help My girlfreind thinks i cheated on her?

There are rumors going around my high school and shuch and i lied to her before ik it was wrong but i got nervous and freaked out becuse my ex gf that i was with for almost a year wanted to hang and we were hving a rough time and i left school and we went out to lunch and i told her that me and her hung out not that we went to lunch this girl im with means the world to me i cant lose her i deleted my exs num and told her we cant be freinds i dont have much of a family and shes all i have ill do anything to prove to this girl im truthful please anything might help