Head to your Withdrawal section. If your withdrawal is pending, you may be able to cancel it by clicking the 'Cancel Withdrawal' button in the bottom right corner of the screen. After clicking, your funds will drop straight back into your balance.
Step by step...
Click your profile tab in the top right corner of screen.
Head to your Withdraw section.
If your withdrawal is PENDING, you should have an option to cancel it by clicking 'Cancel Withdrawal'.