Looks like you have done it right. (I even see you taped the other end of the heattape to prevent electrocution if someone touches that end).
are you plugging it into a thermorstat or directly into the wall? Either way, I would suggest to try plugging it directly into a different wall outlet. Perhaps the power source you are using is not providing power.
If you are using a known-good wall outlet, then the problem must be the quality of the connections. They appear to be "wired" to the correct points. But maybe they just still aren't penetrating the plastic coating inside BOTH of the 2 clips. If EITHER clip is not penetrating to the metal inside, then there is no current flow and no heat.