I think the fact you've got some motivation and that you are still easily distracted means evidently that motivation is not strong enough for you to resist the temptations and distractions, and perhaps your motivation is not specific enough to motivate you. I think my top tips are:
1)Establish much more specific short term and long term goals to achieve your ultimate goal-your motivation. Make sure that the ultimate goal(s) is what you genuinely want to achieve, not what your parents/teachers/friends expect you to achieve. Having a realistic and intrinsic motivational goal will help you immensely.
2)Try to have a to do list day by day listing all the things you must do and other optional things you need to get done-school work and other commitments-avoid procrastination by using surfing the net as a reward another a successful study session, for example, and keep it to 5-10 minutes for every 45-60 minutes of high concentration study.
3)Enforce some self-discipline, whenever you get distracted, visualise yourself at the end of the HSC year, achieving all the goals you want, and having no regrets. Smack your desired ATAR on the wall-and whenever you are distracted, look at that number-and think to yourself-if you want that ATAR, you will just have to keep working hard and keep studying
4)Make sure you are taking care of your body. I.e. have adequate sleep and regular sleeping routine, rest well, study in times where you are the most alert, eat healthy food, exercise and establish achievable goals for each study session where surfing the net or a quick snack is the reward for successfully achieving the study objective of that session as well as regularly do some physical exercise.
Basically, during the school term, I basically studied by doing the following:
1)I would assign at least 90 minutes of rest after school-so it is like 30 minutes for afternoon tea and 1 hour for dinner, I would make a to-do list of all the things I needed to do that day-preparation for assessment, homework and study(extra questions), it is usually on the subjects I do on school that day-and the list is always slightly longer than realistically what I can achieve-because I want to push myself to maximise my time efficiency
2)I would take a 5-10 minute break for each hour of study, and during that time, I would either re-hydrate myself or procrastinate on the net to relax and refresh myself-time management and planning of each session-whether mentally or on paper is extremely crucial
3)I would write down any questions I found hard or I didn't understand, and I kind of regret the fact I didn't ask these questions the very next day, but basically I would accumulate these questions, say over a period of several weeks, by which I would then ask the teacher in one go or I would try to solve the questions myself
4)I would also try to do practice papers and past HSC exam questions on the topic I was studying for-whether it was chemistry, physics or maths as soon as possible(I.e. when I did my textbook questions as well as other extra ones)
5)I would often set aside the weekend for more intensive studying/practice/reading ahead, but in general, you have to consider whether the homework will be beneficial to your understanding-because sometimes teachers set random homework that wastes time and doesn't add to your understanding, and under these very rare circumstances, I choose not to do it because of the often significant amount of exams/assessments tasks I had to study for-prioritising is everything
But I think the most important element of studying efficiently is to listen in class to what the teacher have to say, because if you understand the content in class, you don't have to waste the time to re-learn the concepts yourself at home
Having provided all this advice, however, I think the most important thing is for you to do right now is log off BOS and just focus on studying for that maths extension two test(because you are evidently distracted by the internet easily)-pay particular attention to the mistakes you have done in the past and avoid MAKING THE SAME MISTAKES tomorrow and just looking over working out for the harder problems. Don't unnecessarily panic yourself by doing more new questions. Hope this helps and I wish you all the best for your HSC and your maths extension two assessment tomorrow