This is why I love having a machine with a drop in bobbin that also has a clear bobbin cover plate. It takes clear bobbins so I can always see how much thread is left on the bobbin, HOWEVER....I have STILL ran out of thread! The most I have ever sewn without bobbin thread was a block and a half. I have ran out of bobbin on long seams when I thought I had "just enough" It is really bad when you are using your spool thread in your bobbbin and you have "just enough" on the spool and your bobbin runs out. That SUCKS! lol thats when you say THWI and fill the bobbin with a different thread! lol I usually try to fil several bobbins at once so I don't have to unthread and rethread or take the time out to refill bobbins!
Good luck getting it finished!