Can I use a 3-way switch as a single-pole switch?
Yes it can work.  3-way switches are spdt (single pole double throw) with 3 screw terminals, and regular switches are spst (single pole single throw) with 2 screw terminals.

Just pick the correct two contacts and you are good to go.  .  

If there are two on one side and just one on the other, then connect to the one that is alone on one side, and either of the other two on the other side.

A multimeter is the quick way to figure out which terminals to use.  Just set it for ohms and you will be able to tell what happens as you toggle the switch.