It should be enough for monitoring yourself, assuming the band is piped through the PA system.
As far as filling that room, that's open to debate. You'll be competing with the rest of the band, plus room noise/conversation (which could be substantial). It's possible you'd have to crank that little thing all the way up, and then it would probably not sound so good.
I'm a keyboardist and I use a keyboard amp that's 300 watts. I've never need to crank it over halfway up. So I'd say you might want an amp around 150 watts, to give yourself a little headroom.
I also carry around a little piece of 2x4 in my gig bag, which I use to tip the amp back. That aims it better for the ears, and also de-couples the amp from the floor a bit. There's not always room for a chair, and sometimes that doesn't look good from an audience perspective either. It just depends on the gig, although I have set my amp on chairs when I could.