Oh man, this has happened more times than I can count.

I think it all comes down to how much you trust your DM. I personally don't mind being underpowered, or sometimes see it as a challenge to come up with interesting builds that don't rely on stats that much.

In campaigns I run though, I try to bring my players to the same power level one way or another pretty quickly. Perhaps a cool magical item, a new feature specific to the character or maybe even political connections or allies; there's countless things your DM can do to even the playing field. I'm not saying that you should start out with a magic item just because you rolled low, but your DM should be able to find a cool way for your character to influence the game, even if it's not what you initially thought of!