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Access to HE grading? help pls

Hi everybody ,i am on Access to HE for art/design and got conditional offer that says : successfull completion of curent course and i dont know what does that mean ?
i dont understand the system/grading on that course and i am not shure if i'll be able to complete as i didnt handle one unit that was optional and been told that was a last chance to handle in -all work from term 2 had to be handled this week.
i had many work to catch up from term 1 ,rework my portfolio for different subject for interview on uni (i changed course subject just while ago and so whole portfolio had to be rebuilded).and i managed to handle in all work from term 1,and from term 2 but just one unit is missing so there will be no pass.
does that mean that i will not have anymore chance to handle this unit on later stage ?
also i dont understand credit system ,i have to achieve about 47credits at level 3
but how is it counted?can it be counted also from late submitions?
if i dont pass the unit ,it means i will not achieve diploma so i'll not get on that UNI?
there is lot of work to be done within couple weeks and i dont have the will to make it as i am just thinking negatively.
there is no doubt this course was for me as mature student mostly waste of time and i didnt enjoy it on beginning because i was focusing on fashion design instead of what i want to do now. it holded me back,no enthusiasm,didnt take it seriously,tutors not much supportive, but i know its still my fault i didnt keep up with work so i get overwhelmed now heh
can somebody explain me how the system works?
i was reading on forums that to finish it successfully i have to just gain certain credits ,i dont need to pass,or there might be last chance on the end of course ?
also if somebody can explain me how those credits are working.