Why does the ijekavian 'ije' vs 'je' keep tripping me up in writing?

I’m a false beginner who can decode basic Bosnian texts, but every time I try to write a simple sentence, I second-guess whether I should be using 'bijelo' or 'bilo'. It’s making me freeze up during actual conversations because I’m too worried about spelling errors. Is there a simple rule of thumb for this, or did most of you just memorize the vocabulary as you went along?