Hello,

The eligibility criteria for appearing in UPSC prelims is as follows :

• UPSC does not discriminate against candidates based on their scores in graduation. Hence, there is no minimum qualifying percentage as the IAS eligibility condition.
• You must hold a graduation degree from a government-recognized university.
• In their final year or awaiting results, you are also eligible to appear for UPSC preliminary Examination.
• A citizen of India

Hence if your third year is your final graduation year then you are eligible to appear for the exams.

https://competition.careers360.com/articles/upsc-ias-syllabus

You can refer to the link provided above for more information.

Hope this helps!!