Answer:
This passage contains many errors. Here's the correct way of rewriting this passage with correct grammar, spelling and punctuation:
Sam knew that staying up late on a weeknight would affect his exam performance the next day. However, he believed that his friends would be mad at him if he didn't join them. Peer pressure and the thought of losing his friends scared Sam. He planned to meet them for a couple of hours and then leave early to study for the exam.
Step-by-step explanation:
The first sentence contains the word effect which is incorrect. Instead, it should be affect.
The second sentence has a misplaced punctuation mark. After the words mad at him at the end of the sentence wit the misplaced punctuation mark, there's a period which shouldn't have been there. With this misplaced punctuation mark, the sentence is a fragment or an incomplete sentence. Instead, the period should be removed and the If should be in common letters as well.
The last sentence has a error as well as it has the wrong word. The word should've been to and not too.