The absolute 100% grade is not just a matter of skill and performance but it is also based on many other things sometimes including luck.
For example, there are many times additional requirements that are not described on the assignment draft and are given to the students verbally. Even if you implement 100% of the draft, your grade may not be 100%. If you want a flawless grade, you will have to participate and ask many questions to the tutors so as to understand what they are asking and if there are hidden requirements.
Please note that if your skill is not high enough, setting as a goal a flawless implementation within a strict deadline is a very bad strategy because there is a high chance you will not be able to understand all the details within the time frame given.
A fail safe goal for beginners would be a grade around 60-70%. Then try to build skill gradually from there.