Loft - how to modify guide curve

Hi Everyone,

I'm having trouble creating the profile I need using the loft function. This part is supposed to look like a funnel that has a square socket where a stepper motor will fit. I've drawn the profile sketches and made the loft but the result shows curves where I'd like a straight profile. I can grab the green points on the loft profile guide line and drag them around but I can't control the shape of the spline curve they generate. I also tried (not shown here) making my own guide curve and that worked really well but only for one side of the part. The loft always used my guide curve for one side of the part and the self-generated guide curve for the opposite side. Maybe there's a way to simply turn off the automatic guide curve?

Thanks for any help you can give. I'm new to Solidworks and using a student licence, if that gives you clues.

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