If your draw length is 28" and the bow is correctly marked 45# @ 28" you can try the following before referring to the spine chart. Start by determining if the arrow is left or right of a vertical line. Draw a vertical line on paper or cardboard, then stand 10 ft and look down the shaft at the vertical line. If the arrow is left and the arrow is stiff and vise versa. Since the arrows are cut to 29", build the rest out by adding tape, and/or add weight in increments of 25 grains to the point, and repeat the process until you are hitting the vertical line. If you are right, the arrow is weak, and you can try a lighter point, or a stiffer spine. Once you find the right arrow and assuming you want to try paper tuning, start with the information from Elite Arrow. If you want to check and compare arrow spine, checkout the chart at 3Rivers. According to their chart for 45 - 50 lbs. your choice includes C-D which is shown below as a 1916 or 2013. I would recommend skipping the 2013 unless you know how to straighten arrows. The 1918 is a little heavier and about the same spine. Here are two links for more information.
http://elitearrows.com/proper-arrow/https://www.3riversarchery.com/pdf/ArrowCharts.pdf