Try cutting off about 1/2 inch from the end of the bag. It is possible that the very end of the roll was compressed when rolled. Also, make sure you have made a straight cut. Check to see if you have the end of the bag over the gasket or into the vacuum channel. It should only go up to the gasket, no further.
- When you get to the end of a roll of bag material, why won't the bags seal?