Wiring a 220 outlet- can I use a 15 amp outlet with my 20 amp breaker? Or should I get a replacement 15 amp breaker?
You may know that on 120V circuits, you are allowed to use 15A receptacles on a 20A circuit.  This is a special exception that only applies to 15A receptacles only on 20A circuits.  

The Code says nothing about voltage.. You can use exactly the same exception on a 240V 20A circuit. You are free to use 15A or 20A receptacles (NEMA 6-15 or 6-20). 

If you use a 20A receptacle (NEMA 6-20), the 15A plug will fit in it just fine.  They are keyed to do that.   (Just the same way as 120V NEMA 5-20 sockets will accept the common NEMA 5-15 plugs.)

There is only one gotcha: if there is only one socket in the whole circuit, the socket size must match the breaker size.  So if you use a NEMA 6-15 on your 20A circuit, make sure it's the usual twin-socket receptacle, don't use a one-eye.