When I rescale I start with the target scale (35), and divide that by the model scale(25). That produces the percentage change to print.
35/25=1.4
that is 140%
Test print a page that has a control part, that is a part that you know the size of. Measure that control part to verify that the scaling is correct. If it is, build away, if not; find the percentage difference of the control part to the prototype. Multiply that percentage to your previous number (in your case the 140%). Print that same page at your new target percentage. Measure the control part. Continue this until you can live with the results.
Remember that scaling up requires larger pages or tiling parts. I try to avoid scaling up more than 300%.
I hope to see the results of your build!