I'm a 16 old student and I'm getting weird and intrusive thoughts which are unwanted and unintentional. I got those thoughts about buddha which can be greater insult for Him. But none of them are intended or wanted. Do this collect bad kamma? I've begun to fear those thoughts as I'm someone who fear sinning more than anyone. Please help me, what should I do?
There's no sin in Buddhism. Buddha will not be offended if you're thinking some silly thoughts. Don't hurt yourself with this fear. No need to perpetuate those silly thoughts either, it won't do you any good. Focus on what's beneficial. Such as study of Dharma.
Karma is not watching you, it does not revenge or punish. Karma is the future you build with your choices, day after day after day.
In the teaching of Dependent Origination, intentional thought arises at the 4th condition called 'nama-rupa'. The unintentional thoughts that arise prior to this, at the 2nd condition called 'sankhara', are the product of ignorance (SN 12.2) and/or past becoming (MN 9).
Therefore, weird and intrusive thoughts ('hindrances'; 'asava') which are unwanted and unintentional are the inevitable results of past becoming (MN 9) and kamma (AN 10.61). Not wanting such thoughts cannot stop their arising because the arising of such thoughts follows the law of Dependent Origination; which is a fixed absolute law.
Your questions on this forum appear to show a conflict between internal personal desires and the desires of your mother making you make promises to the Buddha. If you live with your parents, you must generally obey most of their directives when their directives are reasonable. Buddhism clearly teaches Buddhist parents have a duty to "protect" their children from harmful things (DN 31).
However, being forced to make promises to the Buddha is not proper. Instead, whatever concerns your mother has about your actions, your mother should clearly explain why such actions may be harmful & dangerous for you. If your mother is unable to do this, making promises to the Buddha is unlikely to be effective. Therefore, it is natural for your mind to rebel against or reject anything forced upon it; including rejecting the Buddha.
Rejecting the Buddha does not really collect bad kamma. What collects bad kamma is the underlying reason why the Buddha is being rejected. For example, if the Buddha is rejected to justify engaging in drug taking or sexual misconduct, the collecting of bad kamma will be caused by the drug taking or sexual misconduct.
If you are a young person, it can be difficult to understand lust, let alone give it up; because nature creates lust to control the mind of teenagers/young adults. If lust did not control the minds of young adults, young adults would not have sex and make babies. For most of history, most girls were married at 16 years old and had children very soon after. But today, young people accumulate lust because the corporate society makes money from trading in addictions. Today, most young people believe sex is for entertainment rather than for reproduction. Of lust, the Buddha said:
When a person lives heedlessly, his craving grows like a creeping vine. He runs now here & now there, as if looking for fruit: a monkey in the forest.
In summary, it is expected in a society with birth control and pornographic entertainment that young people fight against their parents and fight against the Buddha; unless their parents are immoral sexual liberals. In Buddhism, this is called "amataputtikabhaya" ("danger of not having parents").