Not really bro, if you are saying there are people who fuck around in your cohort that means it should be easier for you to score a higher internal rank say for example first. If you come first then your internal mark is the top external mark, which if you studied hard, would be your external mark
And if youre saying there are only a few people who muck around in class and dont try, their external results will only affect your internal results if you have a really poor rank. Trust me at a selective school like mine there are still people who muck around and dont study for the HSC. Im guessing your school would have a greater percentage of kids who dont try very hard but then it should be easier for you to gain a higher internal rank