I tried plotting Height vs. Temperature, since that is what your plot shows. But my graph looks completely different from yours.
r = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/652735/Results.xls','Sheet','Test Piece 1-BS 1');
Perhaps make it easier for us to help you, by only uploading the two variables you are plotting above, in a MAT file?
EDIT (in response to comment):
I've uploaded the new data file. Also, this whole thing should have been a comment rather than an answer. But I'll leave it here.