Can you finalize an almost-full DVD?

I have about a minute and a half of empty space left on a Maxell DVD-R disc with almost 4 hours of material recorded on it. I recorded it with a Sony DVD recorder and I'm trying to finalize it on the same DVD recorder. For some reason, it won't finalize... Is there not enough empty space? Do you need more empty space to be able to finalize it? Why is this happening? Please help!!!!!