Unless you have been a victim of writing the wrong word of a Seed down or the incorrect order of it, you do not know how frustrating and desperate such a mistake can make you feel.
When creating a new Seed, always double check its validity. Not only by writing it down and double checking it with your own eyes. To me, even if the Wallet checks two or three words, it means nothing. There could always be an error and I try to minimize it.
The way I do it is as soon as I write down the Seed, I close the Wallet, then re launch it and use the Restore option. Enter the Seed from the paper I just wrote and go from there.
I wrote words in the wrong order before and at first glance it looked right. Next time I had to restore my Seed from my paper, it said it was wrong. I got desperate for days, until I tried to swap the word with the previous and luckily it did work for me.
Check your Seed twice. Do not be lazy.
It's like you actually saw what happened to me

because I have faced this kind of situation and just like you stated it, I even wrote the phrase down but didn't do a back check to confirm if the words are correct enough although at the first import of the phrase, I actually was minimizing my phone and checking the phrase I wrote on keypad and inputting it to the space on the wallet and after the wallet was successful created I wrote it down but unknown to me that the words I wrote down were not in the same order(spelling) and later found this out when I actually changed my device to which my wallet was and in puting the phrase to this new device the error of wrong phrase keep popping and believe it was like a nightmare I wouldn't want to relive so I tried changing some of words and luckily for me, it was a misspelled word that was the case for my own.
so doing a double check on seed phrase is something that worth it, you never can tell what error you might have made #dontbelazy