Getting Different Results For Nozzle Geometry

[Pegabug]

Decided today I would go through the math and validate the geometry that RPA (Rocket Propulsion Analysis) software spit me out. All was pretty close, with the exception of mass flow rate being ~1 kg/s higher with RPA's computed data for the same thrust force.

However, when I got to determining the throat and exit area I got two widely different results. Attached to this post is a screenshot of the solver sheet used to compute everything. The SOLVE section is where I perform the equations in Rocket Propulsion Elements 9th edition (Chapter 3). The Compare section is the data from the RPA software.

For those who just wish to see a brief overview of the difference:
Solved: Dt = 68.5mm, D2 = 183.4mm, Aratio = 0.1396
RPA: Dt = 109.7mm, D2 = 301.6mm, Aratio = 0.1323

Why would there be such a huge geometry difference between the two? I don't think there is an error in my solver sheet, I followed the example problem exactly and didn't see any typos. Granted my analysis was for an ideal configuration and there's isn't but a difference that large is clearly something more.

Which should I trust? I was using RPA to help do the thermal cooling analysis, but now I am hesitant and may need to throw out the design it came up with and do everything by hand.

NOTE: This is for my senior design project, if anyone has free time and has worked on rocket engines before, I would greatly appreciate any guidance on engineering them (all aspects).