Sounds like you really did great!
There is no problem trimming excess off your borders. I personally don't like to find that I cut my burders a little shorter than I needed, which has happened. I hate piecing borders unless I can make them all look like I planned them that way, so I have to redesign and use cornerstones or piano keys if I don't have enough fabric to cut all new one piece borders.
You got it right, and that's all that counts.