What type of sled are you using? One that has you tilting your blade to 45, or one that holds your work piece at 45, and keeps your blade at 90? I built a simple one over the weekend that has me tilting the blade to 45. I can make a more accurate sled that way, less to get wrong. I use the 5 cut method to square the fence as best as possible with the blade still at 90, then, once the fence is square, use a digital angle finder to set the blade to exactly 45 of the table bed. If your joints are coming together nicely, but the end result is not square, most likely your blade is slightly off of 45 (or if using a sled that holds your work piece at 45, either your sled is off of 45, or your blade is slightly off of 90. If your joints aren’t coming together nicely, then the surface your registering your work piece against isn’t square, or it could be a combo of both.