Not sure if my sins are forgiven...used to masturbate and i quit. i asked for forgiveness many times but not sure that its accepted because of the ruling of taubah, sincere regret and intention

im 16 and i used to masturbate and its been 4 months since i quit i asked for forgiveness many times but not sure that its accepted because of the ruling of taubah, scincere regret and intention, the problem is IM NOT SURE if i done those i remember being scincere by admitting what i done without a good reason and i said that its a horrible act and i also made a firm intention of never doing it again plus i also offered salat-al-tawbah (2 nafl) is this good enough? that goes for other major sins i commited and tried keeping to my intention by not missing salat w/o a reason also im having disbelif thoughts, i know its not me its the work of the shaytaan, but its bothering me what shall i do? also im getting my GCSE Exam resultson thursday and i dont want to tellthe truth to my family and other people, i know i cant lie what shall i do? please do a dua so i dont have to lie