Be ambitious, keep climbing and always have hope. Beware of falling and remember that life is minutes and seconds. be like the ant in hard work, patience and perseverance. Always keep trying and keep repenting.
If you go back to sin then repent again, memorise the Qur'aan and if you forget it, go back and memorise again. The main thing is that you should never feel defeated or frustrated, because rationally speaking there is no such thing as the last word or the bitter end. Rather there is always trial and error and learning from your mistakes.
Life is like a body that may undergo cosmetic surgery; it is like a building that can be renovated and rebuilt from scratch, with new decor and paint.
Do away with all thoughts of failure, and stop thinking of calamities and problems for Allah (swt) says:
...And put your trust in Allah if you are indeed believers. (5:23)
May Allah (swt) bestow upon all of us the most sweetest form of sakeenah and patience and may He make us all of the dwellers of Jannah! Ameen!