You don't have to write "to be continued" on your pages. Normally the examiner can tell if you are continuing on extra paper and they can press a button on their marking interface to alert the exam board about it, or when it reaches the exam board's processing stage the staff there will know if extra paper has been used and they arrange for special marking or something like that.
I also used many sheets of extra paper in my exams and I was assured by staff that all papers are checked by two people. One person does the initial checks for extra paper/incorrect details etc and another person double checks it before it is sealed and sent off.
If on results day your grades are lower than expected, I strongly suggest reminding your teachers that you used extra paper in the exam and they will see what they can do when they contact the exam board and apply for a remark.