PSU to Motherboard connection not in all the way

Trilla90

hi i got a new custom pc from hardwareversand and it was finally delivered today. I've never built a PC before so I got them to assemble it, only i ordered a psu separately from dabs.com (something i regret doing right now )

anyway the motherboard is an an ASRock 970 Pro3 R2.0, AM3+, ATX
and the PSU is a Corsair CX 500

i got the PSU installed into the pc case without any problems. Then i had to connect the PSU 20+4 pin connector into the motherboard. It goes in most of the way but it won't fully latch on and there's a slight gap in the bottom.

The PSU pin cable has a latch that is meant to wedge itself under a ridge where the motherboard pin connection is but i can't get it to go under. I've tried forcing it down as hard as i can, but obviously i don't wanna snap the motherboard either.

It is attached, only for the small gap, so i'm wondering if it will still work the same or would i need it 100% attached for that. I've even resorted to filing down the ridge to get it to fit (probably a stupid idea) but still can't get it under. Any help would be appreciated

http://imageshack.us/a/img843/56/mf50.jpg
http://imageshack.us/a/img17/2268/y3uv.jpg
http://imageshack.us/a/img707/9699/h26h.jpg
http://imageshack.us/a/img4/6489/yim6.jpg
http://imageshack.us/a/img18/7614/pj2u.jpg

whizbang

Pull it out and inspect very closely the contact pins and sockets at the tight end.
Hopefully just small a piece of packaging dirt, Maybe moulding bits left on the plastic.
Does the 20 plug properly without the extra 4 pin. ?