It's the quality setting & how you go about it. A 4.7 GB (gigabyte) disk can only hold about 4.36-4.37 GiB (gibibytes) in real terms. DVD info
If your softw only allows 75 mins & doesn't have any options to change the capacity, then I'd dump it & get something decent like Nero 7 or Roxio. These will allow you to add over 2 hrs of video on a single disk. In fact, over 3 hrs if you don't mind poorer quality.