Hello and welcome, Thank you to show us you run on the forum before doing anything x).
More seriously, I'm sorry to tell you that but we can't do a TAS in one week x). And here, hum, I know you didn't put a lot of work into this but it's more like a good casual play which do not beat the human World Record (
https://www.speedrun.com/nsmbds#No_Secret_Exits). I saw some mistakes here and here but I can't watch the all run because for me it desyncs :/. I know you didn't watch addresses of the RAM to your speed because you just watched TASes on Youtube, it's ok.
How to make a proper TAS :
learn everything about TASing (there are guides on the site and we are here if you have questions ) and the game you want to TAS (videos, speedruns, informations on the site etc).
If there is no TAS on the game (here it's not the case :
[3320] DS New Super Mario Bros. "warpless" by Hartmann in 39:39.95,
[3512] DS New Super Mario Bros. "warps" by Hartmann in 20:23.85), figure out RAM addresses and RNG if there is one.
Make your routing for you TAS not only in the level menu but in levels (if you can go to the upper way or the downer way : which one is faster ?). After, begin your TAS and level by level or part by part, you'll try every single possibility you think to save the faster way and do it for all next ones !
I hope I helped you.