I also had a similar situation, I was trying not to get too worried about it as my TA kept telling me from day 1 that your guests will always wait until the last couple of days before the deposit is due to book.
My fiancé and I used paperless post for our invites, it was efficient, had what we needed and allowed us to track everyone's RSVP online (we could see when people opened the invite) and send out messages. This came in handy when we were a month before our deposit deadline. I sent out a reminder message to just those who were marked as "Attending" and those who had just opened the invite but hadn't RSVP'd and left out those who sent their "Regrets". Before I sent this out we had two deposits and the week after I sent out the reminder the rest of our room block was booked! It can happen ladies, sometimes they'll surprise you.
It really shocked my TA - lol. We did run into a different problem though, our rooms were going so quickly and we found out that our resort sold out of that room category for our dates. I scrambled to text all my close family and bridal party to get their rooms asap and most of them did.
Now we're about 2 weeks from our deadline and we don't have any more rooms held. Luckily the resort released a couple more rooms (my TA has been calling everyday about it-love her!). I'm a little worried that some of our stragglers will be stuck paying a lot more for suites but hey the "early bird gets the worm".