Begin writing short fiction before writing novels?

What should you do? Follow your heart, and your pion. Don't be put off writing novels just because you didn't get it right first time. Geez, I have literally billions of words' worth of unfinished stories and screenplays, but it was all part of the learning process that got me where I am today (selling my first screenplay!). It's perfectly normal for a writer not to finish every story. So accept that you're not perfect and keep working at your goals. It's really up to you to decide what those goals may be. Like I said; follow your heart.