Participating in school will be one of the big obstacles to overcome in your search for better school marks. It may take significant planning and risk, depending on the school and the area it is in. If you do not get negative feedback from classmates try participating in class with questions, answers, suggestions. It will keep you awake and focussed and, more importantly, it will encourage others to join in in a positive manner. What can happen? Well, you could learn more, the teachers would be more helpful when you needed guidance or assistance, you may get leadership approval from your peers. Many positives are there for your taking, not to mention that key of higher grades.
Sometimes you may need to seek approval from some people first if that will help. See if some of your friends may be encouraged to support you with the occasional answer or question, or even some homework done on time. Anything that may improve the learning environment will benefit.
Is it possible to start a study circle. This gives you the opportunity to be a leader, meet new and valuable school contacts, and have more sources of help and interaction. These can be small groups of peers who you can rely on. Meet on or off campus. The relationships formed in these groups are often long lasting, threading way into the future. You can use each others notes and ideas to advantage. Be reliable. Be useful. Be that leader. Make sure everyone's input is valued. Make sure everone has a turn. Make sure there are no put downs, even in fun because you never know how the other person may take it. The individuals in study circles tend to grow rapidly in maturity.
If the classroom is out of the question as a place to stand out, even a little, try putting something back into your community by offering to do a small extra job around campus. It might be that only a few notice at first. It seems that if you put a positive spin into something, the universe in some way rewards your actions. So once you feel a bit more confident about your power, take it into the classroom and work on your academic capability. Do not go for nerd of the week. Go for the likeable all rounder. This is a better target. You are looking for a more comfortable and more enjoyable learning place, that's all.