When I was a 1L, I had about a 10:1 letter-to-interview rate. So you may want to expand your search. Or just send out the letters to your preferred location now, wait a week, and then send out the other ones if you haven't heard anything.
how many did you send out?
Forty-five letters to district judges. I edited my earlier post; ratio was closer to 9:1, but more like 8:1 if you include the "please submit grades, and we'll review applications in February/March" responses. (I sent letters out Dec. 1 and requested interviews over the break, so I never sent grades out.)
Keep in mind that many state appellete courts aren't in session during the summer, so the experience is going to be different. That said, don't entirely discount state court judges. A few friends of mine interned with state trial court judges, and they all had a really interesting experience. Wide range of work involved, there.
This is great advice; don't discount state judges. I split my 1L summer with state and federal judges, and I appreciated the different experiences. But not all state appellate judges are "off" for the summer, and even if they aren't sitting, you will likely still do substantive work.