I think it's helpful to know that Buddhism is described as a "threefold training" -- virtue, mind, and wisdom.
If meditation is mostly "mind", perhaps self-control is more to do with "virtue".
They are related but it is worth knowing that there is more to Buddhism than only meditation.
One of the things that will eventually help self-control is "wisdom" (right view): when you (more or less correctly) "view" the worth or worthlessness, the benefit or non-benefit, of a behaviour (e.g. of "waste a lot of my time in youtube watching documentaries") then you might modify that behaviour ... because you'll want to do more of what's beneficial and less of what it isn't.
Self-control is related to "virtue". The five precepts are (just) a beginning in terms of what's virtuous ... all necessary but maybe not sufficient. For laypeople there are suttas which describe what a virtuous lay life can look like (e.g. the Sigalovada Sutta and others) -- activity that's contrary to these suggestions (for example, "compulsive gambling") is probably un-virtuous (and regrettable) even though it doesn't break one of the five precepts.
Virtue might be related to meditation. I've read that when you start to meditate, you'll be disturbed if you're not virtuous: that it's important to get the "virtue" part of the practice happening in your life, perhaps even before you meditate. So maybe it's not that virtue (including self-control) results from meditation, it's that virtue enables meditation. Maybe the causal chain is more (approximately) like this:
- Virtue (having done right, and developing self-control) enables Mind (meditation)
- Mind (meditation) helps to change your views and reactions e.g. Wisdom
- Wisdom (right view) helps to cause beneficial behaviour and self-control i.e. Virtue
I have found this sutta helpful, Kimattha Sutta: What is the Purpose?
- "What is the purpose of skillful virtues? What is their reward?"
- "Skillful virtues have freedom from remorse as their purpose, Ananda, and freedom from remorse as their reward."
- "And what is the purpose of freedom from remorse? What is its reward?"
- "Freedom from remorse has joy as its purpose, joy as its reward."
If something causes you remorse ("I wish I didn't waste a lot of my time in youtube watching documentaries, I regret having wasted it") then you might think something like, "This is remorse ... and instead of feeling this remorse again in future, to gain freedom from remorse, t would be better to develop the 'skillful virtue' of practicing more beneficial activities instead." When the occasion arises again, you might remember, "If I start watching youtube again as I did before then I will eventually feel remorse again, so make a different decision (do something different instead of falling into a repeat of that regrettable behaviour) this time."
Furthermore, apart from meditation there are mundane tools you could choose to use to affect your worldly behaviour. If you want to wake early, for example, you can use an alarm clock. If you don't want to watch youtube you can configure your computer to block connections to youtube. You might find it easier or helpful to avoid entering a situation where bad/addictive behaviour is an option/temptation.
Also (and I know this wasn't the question you were asking) but "I have planned my life and want to stick to it" could possibly be a mistake ... it might imply ego, and attachment, and self-view (see the answers to this question).
Another reason it might be a mistake: imagine a child who says, "I have planned my life and want to stick to it"! Being a child, they don't know. Similarly if/while we're unenlightened then we don't know.
Another reason it might be a mistake: the situation that we're in changes, and is to some extent outside our control. So a plan that's made for today might not be so appropriate/applicable tomorrow.