Generally speaking, you are considered as a full time student if you enroll in school for at least five months in the tax year.
However, each school defines "full time" in its own way (usually in terms of the number of courses or hours). Is September the normal semester begin date for your school? If so, then you can consider yourself full time if your course load is classified as full time by your school and answer 'yes' to the full time question.
The cut off is the calendar year. 5 months in 2017. In general, universities have enrollment along the lines of Aug-Dec for Fall and Jan-May for Spring. This makes enrollment in either semester 5 months and meets the requirements.
Is your university a qualified educational institution? Do they receive financial aid? You can check the link below.
I presume you are being asked if you attended the university under the Education section. Your university has to be a qualified educational institution (on the list) to be considered for the deduction/credits. Answer 'yes' to the full time student question if you carried a full credit fall semester according to your universities definition of full time.