bridge help!! what am i doing wrong?

i haven’t played acnh in such a long time and now not understanding how to lay a bridge!!

i want it 4 long bc i want to have it centered with the lighted arch i have on the ground floor, i tried 5 long but it was too long and 3 is too small, kept saying that i needed to have the right width, so i added cliffs on each side (so i extended on each end) & then knocked waterfalls and now it says “it’d be hard to use a bridge with a cliff so close” 😭

first 2 photos is what i originally did and the last 2 are what somebody suggested, but it didn’t work so now im just stuck and confused 😭