Another line integral question

**The question**

Consider the vector field **F**(x, y, z) = (yz + 1)**i** + xz**j** + (xy + )**k**.

Evaluate along the path C from (0, 0, 0) to (1, 0, 0), following the helix (x, y, z) = (cos(t), sin(t), t) from (1, 0, 0) to (1, 0, 4 ) and then the straight line from (1, 0, 4 ) to (0, 0, 0).

**My attempt**

I first found a scalar potential with the property = **F**, which is

So the vector field is conservative. I noticed that the path is actually a closed loop, so if I'm not mistaken, I can apply the Fundamental Theorem of Line Integrals. Thus, the solution should be 0, right? However my book says -1. :/

Where have I gone wrong? Thanks.