Excess gst paid

Actual gst liability in fy 2017-18 is Rs.2000

client declared gst liability as Rs.3000 in 3B and paid and also setoff against 3000

How can we claim that excess gst paid?

1.can we apply for refund,neither it lies in cash ledger nor in credit ledger due to utilization against excess liablity declared

2.can we show less liability in 3B in fy 2018-19 beforevsep month return and pay less liability accordingly?