Okay, you did it. Either you forgot or didn't know that you needed the adapter that came with the Memory Stick Duo to use the SD slot in your computer and quickly found it stuck. Before you take it to the repair shop or, worse, risk damaging the SD slot by digging it out with an assorted number of tools, follow this handy little trick I discovered wen I did the very same thing (I knew better too - which made it worse)
Depending on your age / vision, you may also want reading glasses and/ or flashlight. Turn the computer off. Unplug if a desktop computer and unplug and remove battery if it is a laptop computer or a notebook computer.
Take the Sony memory stick duo adapter and with the end you insert the memory stick duo memory card in, slide it into the SD slot and over the stuck memory stick duo (IE: slide it in opposite to how you normally would)
Gently wiggle the adapter and slide it out. If the stuck memory card did not come out with the adapter, slide the adapter in a bit further. It should easily come out. If it still did not come out (it should have) then slide the adapter in once again. Take the tweezers and gently squeeze the memory card adapter (the flat sides) making the adapter tight against the memory card and slide it out.