I measure using my border fabric. I first fold top exactly in half, lay border fabric on the fold and lightly smooth to the end of top. Then I mark where it should be cut. Lay other border strip under first and lightly smooth to the mark and pin those two ends together, cut on mark of first strip. Sew onto top. For ends I do the same as for sides. Fold top exactly in half and continue to do as I did for the sides/ length. People do things differently to get the same results.
There should be youtube videos to show how the "experts" do it. Try a few different ways to see what results you like best. My way works best for me. I have been making quilts since mid 1960s.