Is it really tough to score 100 marks is ssc cshl without coaching???

No it is not tough to score 100 marks in chsl exam. You can easily score 100 marks in chsl exam. You can atleast score 42+ in Reasoning, 30+ in english, atleast 10 marks in maths and 20+ in general awareness. You must read topics given in syllabus, and you can easily clear withouf coaching, many online resources are also available. I will suggest you to write mocks so that you will know what type of questions are asked.