TWI/I2C Protocol with HMC5883L Magnetometer with ATMEGA256RFR2 XPLAINED PRO (megaavr)
To move the address pointer to a random register location, first issue
  a “write” to that register location with no data byte following the
  commend. For example, to move the address pointer to register 10, send
  0x3C 0x0A


So, to read from register 0x03 on, try:

Start &gt; SLA+W &gt; 0x03 &gt; Repeat Start &gt; SLA+R &gt; read 6x


(Notice the W in the first SLA+W.)