Germination is usually 10 to 14 days for me so yes, time to go back and resow the gaps. This time try nicking the hard seed coat and soaking the seeds in water for about 8 hours prior to planting out. Haven't tried starting them indoors myself but don't see why you shouldn't be able to sow them directly.

Where'd you get your seeds? Seems like the ones i purchased earlier this year did not have a great germination rate so if yours came from the same place that might explain your results.