Sell it, buy what you've decided you want.
You've not made a "mistake"; rather, you've found out from a first 'serious' bike purchase (I'm making an assumption here) where you are heading in cycling/what you want/need. Nothing wrong with that.
Don't go the 'upgrade' path; the Trek DS series is a fine design, but it is designed to work with suspension etc. and to be a 'cross-terrain' bike. Apparently, that's not what you want. You'll be far better off -- both functionally and in terms of finances -- to cut your losses and move on to something else.
Something to consider: you mention that the bike is a few months old; you might talk to your shop to see whether a trade-in/up is possible??