Weave in knitting ends
Follow neighbouring stitch paths on the wrong side, then change direction to keep the tail in place.
Work the technique
Thread a blunt tapestry needle. Follow several reverse-side loops without splitting the public face. Turn back through another path; leave enough freedom for the fabric to stretch. Trim after washing and inspecting the join.
Try it on a sample
Use two contrasting tails on a small sample to compare duplicate-stitch weaving and a seam allowance.
Check and recover
Pulling the tail tight makes a pucker. Do not trim flush before the first wash; check that the tail cannot slide out under a gentle stretch.