Can't comment on sandpaper other than suggesting you try different brands and see if you can find something better. Autogeek sells Meguiars Unigrit paper I would start with that. Darren Priest once mentioned a sandpaper in one of his videos that he felt was much better than anything else he ever tried. I cannot recall the brand nor which video it was but you could try talking to him and see if he can offer a suggestion. His company is Auto Fetish Detail. Very nice guy and he loves to help people, send him a message.

As for compound, I have never used the 3M compound. If you want to try other products, M105 is a pain to work with. It dusts like crazy and have very short work time. I no longer use it and switched to Meguiars consumer line: Ultimate compound. This compounds cuts a little less, but it doesn't dust and it also finishes better. Other compounds a lot of detailers like are Menzerna's, you should try both and see if they give you better result than 3M's. An other product you could try is Meguiars M101, never read a bad comment about that product.