Welcome to MHF, iBurger!

A regression coefficient of .999294 is pretty good.

It means your data points are pretty accurately on a straight line.

n=3 measurements is not very much though as you probably already surmised.

It leaves a pretty big chance on systematic mistakes that a regression analysis does not cover.

Do you also have the t-test significance value of the slope coefficient?

At the very least that one should be below 0.05 to indicate that the chance that you wrongfully conclude you have a linear relationship, is less than 5%.