Please help me figure out what went wrong on the test day!

I took my GMAT exam on 8 august and scored 600(q-44 and v-28) which is way lower than what i scored on 2 Gmat Prep and MGMAT tests. Any insights into waht possibly could have gone wrong?

Gmat PREp1- 670
Gmat prep2 -690

MGAMt1-610
MGAMt2-670
MGAMt3-690
MGAMt4-660
MGAMt5-680