[Bluejayway]

In my Chemistry lab over calorimetry, I am asked to graph my results from the coffee calorimeter calibration and two trials of metals. It asks to graph the data and find the maximum temperature. However, after I made my graph in excel (the way the lab instructor instructed) and added a linear trendline (attached graph), the y-intercept, which is supposed to be the Tf does not seem right. In my lab manual, the graph's linear trendline goes up the opposite direction of mine, so that the extrapolated value is on 0, but my graph is not doing that. I am very confused because by using the y-intercept from my graph, I am getting a completely wrong specific heat value for the metal in my lab. Any help would be greatly appreciated!