STI shifter question

I am gathering some used parts to build up a winter beater bike. My goals for this little project are to not only end up with a bike I don’t feel bad about riding in the winter (lots of salt and muck on the roads), but build it myself and learn more about how all this stuff goes together without spending a lot of money on top shelf components.

So my question: The used Tiagra shifter I bought is supposedly set up for a triple crank. With that said, would it work with a double crank? I am thinking that it probably would, but I would need to be careful not to shift too far and possibly drop the chain.

It will work fine.You don’t have to worry about over shifting.The derailleur stop wont let that happen.
Cullen