Why can't I remove the top layer to access the internals?

I have an ASUS X555QG, and I want to swap the Hard Drive for an SSD I already cloned. After looking at some videos and ifixit's manual for the X555L, it should come open after unlatching the internal clips on the top cover, where the keyboard and touchpad are. However, I managed to do so for all sides, but somehow, something at the centre is preventing it from lifting up (it's not the ribbon cable for the keyboard and touchpad, since it should at least have some clearance when lifting it open for detaching the cables themselves, but mine wouldn't budge one bit). Did I go wrong somewhere? Thanks!