What should I do about my feeling of fear of Allah’s wrath and my inability to remain steadfast in repenting from recurring sins and transgressions?

The door of repentance is open. Therefore, a Muslim should immediately repent to Allah, regret all their sins, adhere to Allah's Sharia (definition), maintain the obligatory prayers, and avoid disobedience, for "the one who repents from a sin is like one who has no sin." If they return to sin, they must return to repentance and not despair. What will help them in this is accompanying righteous people, constantly remembering Allah, supplicating, and humbly imploring Allah Almighty to keep their heart firm upon His religion, and staying away from everything that hinders them from repentance.