We all go through this where we want to post a picture that's too large to fit in the square but I have a solution!
You are going to have to download the app whitagram, I promise it'll be worth it oh and did I mention it was free?
Open the app and press add photo on the bottom left then decide which photo you would like to use
After selecting the image, it automatically make the photo the perfect size as well as make the background white! But if you prefer to make it another color, its under the edit section!
Now then press "to Instagram" on the bottom right and choose the resolution of your choice :)
Now just choose "open in Instagram"
TA DA! It fits perfect! Continue to edit as you wish and enjoy how easy that was