The weight of carrying this deception for six months must feel crushing, especially knowing you're benefiting at the expense of someone who trusts you enough not to challenge it. You're right that you're "too far in" for this to be easily unwound, but that same depth is exactly why continuing will only make the guilt heavier and the eventual reckoning more devastating. The shy junior who hasn't spoken up yet might actually respect you more for coming clean than you think - and your conscience is clearly telling you that your talent and worth aren't dependent on stolen work.