Sandra, you can use “Collins Miter Clamps” to hold the small end pieces together with authority. They will stay where the clamps hold them and you can adjust them if they’re not perfect. Amazon sells them. Fill small holes with putty or spackle.

You can see how I did that in this post: https://sawdustgirl.com/how-to-trick-out-your-trim-molding-in-5-easy-steps/

It’s hard to visualize sometimes. I keep my pieces vertical against the fence—I’ve found I get less chipping on the fine mitered edge which is important if you’re dealing with prepainted (sprayed) trim. Then I push my blade out to the right at 45° for all the angle cuts. Trim right side up for one side of the returns and upside down for the other side. On each piece, just bring the blade back to 0° and cut once. I’m just no good with bevel cuts so this works better for me.

Which is why I don’t nail them. I’ve yet to have a glued return fall off. Knock on wood.