Your favorite singer may be Freddie Mercury. But if your range isn’t like his, don’t try to write songs that will make you sound like a crackling teenager in puberty. Write within your own gifts. Find a way to make YOUR range sound awesome. Is it the tone? Is it in how great you are at writing a melody? Lyrics? All of the above?
Use your gifts, and DON’T write in a way that makes your look anything less than awesome. You can always work on your range in the background, and if you finally get to that level vocally, you will have earned the right to write songs there as well. The same can be said for any instrument. If you are not a great guitar soloist, learn how to make simple solos sound cool, or just don’t have a guitar solo at all.
Let common sense be your ally, and pride be the enemy, of your greatest music.