Should I tell her? Please give me some advice

so basically i have two close friends (becca and liz) becca i am closer too and we tell each other everything. basically becca and liz got into an argument bc becca got mad that liz told this other girl (ella) something that she didn’t explicitly say was a secret but obviously didn’t want other people to know. becca is quite assertive and stands up for herself so she instantly confronted liz but liz is the type to joke about things and basically laughed at becca and didn’t apologise. anyways fast forward a day or 2 i kind of understood both of their sides so somehow i got in the middle and both of them were talking about the other to me. i was open to both of them saying i understand both sides and im talking to both. BUT the more i think abt it im only beccas side. now here’s my dilemma a while ago i told Liz a secret that becca mad me swear not to tell anyone and i indirectly told liz (indirectly by she guessed through obvious hints). i only remember this secret bc liz said to me “if she knew that i kept the secret u told me she wouldn’t be mad” i felt like this was blackmailly but she promised me she wouldn’t tell becca. but even tho she isn’t gonna tell becca i have a guilty conscience and i feel like i need to come clean to becca. im just scared she will be more disappointed and mad at me and hate me as well. the only thing is we have a month i til i move school for good.SO MY QUESTION IS: do i come clean to becca??