Are chainrings specific to double or triple cranksets?
Absolutely the middle chainring of a triple is different to the inner and outers.  


Tooth profile is different because the chain has to move either way from the middle
Ramps are different - your middle needs ramps on the inside in a triple.
Mount offsets are different too, which is why a triple front derailleur is different to a double.  The amount of cable pull is less for a triple compared to a double.


So if you can return the bad chainring, do so.  If not, and you're willing to modify it, you could try grinding away the tabs a little.   Don't bend them too much, alloy won't like being bent and you'll weaken the whole thing.

Probably safest to list it on ebay and buy the right part - your LBS would be best rather than buying parts on-line.  Plus if they sell you the wrong part, you can return it.