Scaling on horizontal axis is irregular, leads to improper line graph

First time poster here. I am trying to complete a graph for my first year Chemistry class relating Volume & Mass of a liquid to plot a Density line. I have not used the excel graph function in years as I was out of University for about a decade but I am now back to start a new career. Long story short I am finding it difficult to make the necessary small adjustments to my graph in order to make it perfect. Currently my graph's horizontal axis displays each one of my nine data points with equal spacing, which I don't want since the value between each point is not equal. I was hoping to scale my horizontal axis to be similar to my vertical axis where each labeled interval increases by a regular amount, let's say 5 mL, this would give me a more accurate density line from which I could then plot a best fit line to calculate the average density of all my data points. I hope this question makes sense to whomever is reading, I have attached a copy of my workbook. Also if someone could tell me how to add a best fit line and the value of the slope of that line to my graph it would be greatly appreciated.

Thanks for the help, Al Density Plot.xlsx

Thank you very much for your quick reply! Your diagnosis was dead-on, I quickly changed my chart type to scatter plot and voila I now have a perfectly scaled horizontal axis. You would not believe the amount of formatting I was trying to do to fix this issue! If you could let me know if/how I could add a best fit line to this graph & the slope for that line you will definitely earned yourself a round of beers on me!

Never mind the slope stuff. I figured out how to add a trend line and display it's equation on the graph from which I can get the slope form the old y = mx + b formula.

Thanks for all the help, you probably helped me get an extra 10% on my lab report!