It isn't uncommon for people to suffer from the writing like an A Level student problem.
Probably what you need to do is research better - don't rely on text books and basic summaries. That way you will be able to better answer the question rather than doing what most A Level students and weak undergrads do and describe the relevant content but fail to produce an answer to the question. It also isn't possible to do a good 2000 word+ essay in a day or two. I don't know how long you spend on your work but if you aren't spending at least a week or so (not all day every but several hours per day) on major essays then you won't get into the 70s.
Finally, make sure you write and reference well and structure your essay properly (I'm sure that your uni and lecturers/ seminar leaders will offer plenty of advice on this). Stuff like this can seen unimportant but, if you cover the relevant content and make an argument, is probably the difference between a 60-odd and a 65-70.