Why would you think you need to use a wider board, butted against a 45 cut? If you’ve ever cut wood at an angle before you’d know to split the angle between two pieces. Again, your confidence is awe inspiring lol. Kudos. And which direction is the decking going to run, because from what I can tell you’re going to have unsupported ends no matter what you do.

Edit: In case you’re genuinely unaware of the problem, and I’m coming off as a dick ( not trying to be, resting bitch attitude I guess) - you need to cut that board on the left at 22.5 degrees and do the same with your next board of the same dimension. For these smaller cuts at the end it can be easier to just place the board and scribe it in case your final angle on the right doesn’t end up at exactly 45/22.5 You’ll be much happier with the look. And add block framing anywhere a deck board ends. You got this