Runny white sauce?

If your white sauce isn’t thick enough, you can whisk in a little cornflour and water paste or begin again by making another roux and whisking in the runny white sauce in place of the milk. 

Should I grease my baking tins?

This helps stop food sticking. Brush the tin with melted butter or use some baking paper with a little butter on it to rub around the inside of the tin.