Hello,
According to eligiiblity criteria for UPSC Civil Services exam, candidate should have a Bachelor's Degree in any discipline.
Candidates who will appear for the final year graduation exam and will be waiting for the results of their final year Graduation examination can also apply but they should be able to  provide proof of having passed the exam while filling the Detailed Application Form (DAF) for the Mains exam.
So, in your case you will be in the final year of your graduation so, you won't be eligble for UPSC 2019 exam.
You can appear for the UPSC exam after your final year graduation examination.
Good Luck!