You seem to be having problems in your classes, in doing your class work and in completing your homework.

Look at these too. Is the work too difficult for you? Do you understand what is being taught in class? are you doing your homework properly. Do you have any trouble in either the speed of your reading or in reading comprehension? Do you know how to plan your time properly? Are you well organized?

Do you need better techniques in doing your homework?

The above questions may show some of your problems, if any

Your teachers are to be complimented not criticized for keeping you at the end of class. They must feel that you need extra help with your schoolwork and that they can help you. Remember that when they keep you in they are keeping themselves in too. Teachers have lives also. Accept the help graciously and thankfully and without bitterness.

Take a long hard look at your life and cut out the non-essential stuff. Sadly colleges are really just going to look at your GPA. They are not fussed if you played some football or marched in a band. They want to know if you have demonstrated the ability to retain information in the short term and then pass a multiple choice test. If you can do that, you can sail through much of the American education system.

So unless you are so talented at after school activities that you think you can get an amazing college scholarship, then drop out of them. Get the work done quickly and efficiently with good time management. Consider that it will soon be over and you can relax a little.