Scholars say: there are no major sins with tawbah, and there are no minor sins with repetiton.
What does that mean? The one who commits major sins and performs tawbah is forgiven; and the one who commits minor sins repeatedly is overcome by them, and they reach the level of major sins.
Ibn Mas’ud (رضي الله عنه) said: A believer treats a sin as if it is a mountain over his head that may fall on him any moment; whereas a dissolute person looks at it as a fly that hovers around his nose and he waves it away with his hand.1
So work hard to overcome your sins, and never despair. And remember, if you’re not all that worried about your sins, you could be neck-deep and drowning without knowing it.
May Allah (سبحانه وتعالى) protect us from all kinds of sins, ameen.
You can read an excellent concise article on sins and wiping them out here.
(1) Al-Munajjid, Muhammad Saleh. “Do Not Belittle Sins.” IslamOnline.Net. 8 Mar. 2005. 11 May 2006 .