Can't believe it

Unless the missing word somehow changed the meaning of the sentence in a horrifically unfortunate way, or made it completely indecipherable, I wouldn't worry too much over it. I don't think it's a disaster! Agents know typos can happen to anyone.

You've seen it now so you can fix it for all the subsequent queries.
Typos happen. I know it seems terribly devastating, but it's probably not nearly as bad as you think. (The rest is legible, I assume, which is a huge leg up on 90% of the queries that agents get. And as long as you don't have dozens of typos you're probably fine. [I once sent a pitch/query to a publisher and spelled the MC's name two different ways in both the pitch and in the synopsis. >_< He still asked to look at it and told me later it was one of the best queries he'd ever gotten.])
Deep breaths.
In general, because this is a process that tends to make ones eyes glaze over it's usually a good idea to let things sit for a day or two and/or ask someone else with an eye for errors look through something after you make changes. But it does happen to all of us. (When I send a MS to my agent, I always send a second version after he's said "Yes, this is great. I'll start sending it out soon," that has more of the little tiny errors cleaned up. Because I always find extra spaces/missing words/homonyms/typos on a reread. But I need a little time to be able to go through and find them.)
In other words, don't panic. It should be fine.

I sent out a query with two typos in it--in the first para of the letter--and it still landed me an agent.

It's best to avoid typos but mistakes happen. It won't be enough to put an agent off a brilliant book. Try not to worry.

Somehow, one round of queries had a typo in the literal first sentence of the query and I still got requests. I think that as long as it's not riddled with other obvious typos, you should be okay! Just take a deep breath, fix it for the next round, and keep going.

Mine had a basic grammatical error I didn't catch until I already had a bunch of partial & full requests. Agents have been known to make typos themselves - they know we're all human. Hang in there.

Yep, it happens. I just realized that a query I sent last week is missing a full stop between two sentences, making it a super long, run on sentence that's hard to understand. But I got a request from that query! Don't worry about it - fix it up for your next queries and move on.

Don't stress too much, just fix it for the next ones.
I once sent a query to an agent named "Brian," and after sending it, I realized I wrote "Brain."
He asked for a full!

Maybe! I was hoping he just missed it.

Don't stress; yes, it's annoying and you won't make the same mistake again. I have learned that if an agent/editor likes the voice/tone/story they don't care about typos. Eg. The 'full' ms I sent out to agents who requested was full--and I mean full--of typos, missing words, weird stuff I later scratched my head about... really quite embarrassing. (long story but I had to re-write the book after computer died, in record speed). Regardless, I had multiple offers on that book.

Ha ha ha, DL Shepherd. Loved the Brain typo!