In the past, I'd seen many sketches not measured correctly sometimes off a foot or more. As long as the appraiser's square footage is close to the assessor's records, lender accepted it.
Lender rarely if ever go and check on appraiser's measurement. However, if lender had prior appraisal and now I'm doing a refi appraisal, lender could verify the two sketches to see any discrepancies. I doubt reviewers do that.
Sometimes when I measure at say 20 feet 1 inch, I may just round off to 20 feet as long as I have another exterior wall measurement measured to 1/10th foot like 30 feet 8 inches which is more significant 1/10th foot. As long as not all whole foot numbers in your sketch, lenders will not be on your back.