Low census

Hello all. I am a new RN, passed boards in January and started my first hospital job soon after. I've been there 90 days and am finally off orientation (on my own). I feel much more comfortable than to begin with. When they hired me, they hired me for 48 hours per two weeks, or 24 hours a week. I don't want their insurance bc my husband has excellent insurance through his job.
Problem is, they have TONS of nurses that have been there for quite some time. And almost everyone is full time. I took the 48 hours per payperiod bc I was desperate to get my foot in the door there. I love it there, they treat me great. How do I tactfully ask for a full time position? I know I'm the low one on the totem pole, but I would like to fit in with everyone else, and be put on the call rotation. This is the very first time it has happened since I've been there, but I'm afraid of it happening again. Since I started, they've had me on 3 days a week, and last week I only worked once because of low census. One of the girls said that it slows down like that in the summer, too. I really like that 72 + hr paycheck. I am prn at a local NH, but would much rather put in all my time at the hospital. Thanks in advance. I am planning on talking to my nurse manager when I work next, but thought I could use some of your input too!