The speaker is lying in the aftermath of their own mistakes, and it feels physical. They describe themselves as still bleeding, spilling "all over the place," as if the damage is too big to contain. They wait for regret to stitch the wounds, which is an odd, sad idea: regret is supposed to be what heals them, but it only arrives after the harm is done.
Even then, the speaker doesn't expect a clean recovery. Stitched wounds still leave a scar, "a little sign" that nothing ever changes. That line carries a lot of weariness and self-doubt. The speaker seems stuck, unable to undo anything, and says so plainly: "We can't go back."
The ending turns sharp. The speaker stops looking inward and warns someone else, using blunt, angry language, not to mess with a heart, because broken ones "have sharp edges." The hurt person can now hurt others. The mood is raw, bitter, and defensive, with pain slowly hardening into a warning.