Alright, I played your leve, and...
If I'm being honest here, if it's your first level, I say it's a good try, but it could get some improvements.
First of all, some area are too cramped to move & avoid obstacles properly, especially in the beginning and one area toward the end, where you open the door and you're basically attacked by cheeps cheeps from all sides, and imo, I don't think you can avoid getting hit even if you react fast enough, which make it quit....
cheap cheap you could say.
Yeah, gottem.
Also, I'm not sure if this is a oversight of yours or a bug, but the key you get by getting all the red coins doesn't serve any purpose, since you get two keys via killing the two Wiggler next to the doors, and there is only 2 door, obtaining the red coin key really as no purpose, especially since you get the last piece after unlocking the two doors I just mention.
Finally, and it may be more personal than anything I mentionned so far, but in term of aesthetic, some area need more ground to them, idk, on the Wii style, it look weird when there is only one line of ground in the air, in other styles, it might look better, but here, eh, not sure.
Otherwise, I say it was a enjoyable experience, and if this your first level, then don't take what I say here too badly, trust me, I was quit bad at first, but the more levels I made on SMM1, the better I got, so take it as a first step in a long level toward greatness, if your prefer.
Brief, good job pal.