Low grades at school do not necessarily mean you will not be successful in life. You will often hear that you must do well to succeed, but it is simply because good grades make life a little easier. Not everyone is cut out for education, but that does not mean you should not try and that you are destined for failure if things do not work out.
At college there are alternative options to get you grades in the core subjects of Maths, English and Science. There is a lot of support if you know where to find it and are helped to access it. There are also courses more suited to people who are not so keen on the academic side of education.
The world needs a mixture of people to function and there is a career for everyone. With the right assistance, even many people with significant learning disabilities can be given a purposeful, paid role. After a few years of working, grades become less important as they are overshadowed by real life experience. Make the most of every opportunity, highlight the really valuable skills you have learned and do not dwell on whatever letter or number appears beside your subjects.