Here is a great hand build process for the sled…
Getting the spindle on the router dead center is key to cut accuracy. With the ring kit it is easy to check… Park the sled on top of a scrap that is at least the size of the sled. Turn on the router and send the bit about 1/10 inch into the material. Then, with the router still on, carefully rotate the the router. If the hole does not change shape, you are dead on. If you get a slightly out of round hole, you might be ok as long as the sled stays at the same angle most of the time. It you have a “C” shape or a hole that is twice as large as the bit, then make a new sled using the above hand process. You will solve a lot of problems.
Hang in there! Remember, this is supposed to be fun!