It sounds like you're working on Lab 1b, rather than Lab 2b where you've posted this. This issue is answered in the Help Forum under Lab 1b, Step 31. To save yourself time & trouble, always check the Help FAQ first. 99% of all the snags that students run into are already answered there and you can get the fix instantly rather than waiting for us to get back to you.
It sounds like you're working on Lab 1b, rather than Lab 2b where you've posted this. This issue is answered in the Help Forum under Lab 1b, Step 31. To save yourself time & trouble, always check the Help FAQ first. 99% of all the snags that students run into are already answered there and you can get the fix instantly rather than waiting for us to get back to you.