OK......the USB header on the board has connections for up to 4 USB connectors combined in one socket - hence it has 18 pins.
As you look at it on the board from above, Pin 1 is top left, Pin 2 top right and you work down like that until you get to the final pin bottom right which is Pin 18.
Your case connectors have 4 pins plus a separate extra one - you may not need the extra one, but we'll see.
You need to make sure the 4 pin case connector is the right way around (check on the connector or your case manual) and connect from Pin 1 on the header (which is 'Power') directly down the left side....ie Pins 3 (Data- or D-), 5 (Data+ or D+), 7 (Ground or GND) - likewise if you have a second case connector then start at Pin 2 (also 'Power') and go down the top right and connect to Pins 2,4,6,8.
If you have more than 2 case USB connectors then the final 2 headers on the board go upwards from Pin 17 on the left side (Power) then Pins 15, 13, 11 and Pin 18 on the right (Power) then Pins 16, 14, 12 in the same configuration as the first 2.
That should work, however if you do need the final single case connector pin, then place that on the next pin immediately after the first 4 in each case (Signal Data or SGND) - but try without first it won't do any harm.