Hi Michael, Thanks for contacting us! The 42:58 above was referring to the Proportions slider when creating a collage. For creating a Blank Canvas for a 5×7″ photo, simply choose 5×7 from the dropdown (after clicking Create Blank Canvas).
Alternatively if you just want to make a photo fit 5×7″, use the Basic Edits tab > Crop tool with 5×7 in the Constraints dropdown to crop your image so that it will fit perfectly. Let us know if you have any further questions!