Will my repentance be accepted after swearing falsely on the Mus'haf out of fear of the engagement being broken?

Do not take a false oath, whether on the Qur’an or otherwise. Taking it on the Qur’an makes the matter more serious. Strive to avoid it by using techniques of dissimulation (Tawriya) and insinuation (Ta‘ridh). If there is a necessity for a false oath, which entails a legally significant harm, then it is permissible due to necessity. Repentance is accepted if its conditions are met.