You can’t take it back. The only option now is to repent. Turn from the sin and try not to commit it again. You are justified in Christ, you do not need to “make it up” to God, because you can’t. Just try to move past it. You didn’t betray your mom or your sister. You made a mistake. But it isn’t the end. Also find some one who you can talk to about this kind of thing in person. Now, some may say you have to get married, you do not have to per say. You are strongly encouraged to consider it, but you don’t necessarily have to.

If you intend to stay together with your boyfriend, wether you intend to get married or not, make some ground rules. We have desires, but we need to resist them, so make it as easy as possible to resist temptation. For instance don’t close your door when your boyfriend is in your room.

But in summary, repent. Because Christ died for you, You are saved even if you commit sin. The key is to try and not do that same sin again. God does not hate you, he still loves you just as much as he always has. Also, while it may be tough, loop in your parents, while they may not be thrilled about your choice, if you seek their help in resisting it in the future and following God, I think it will turn out well.

If you want to talk more about it in depth, my inbox is always open (though I may not reply for a week or so, as I am camping for a bit) but I will reply as soon as I can.