Solving problems when creating my Gantt chart

It was important that when I created my Gantt chart the period of time for each individual task was appropriate and realistic at the same time. When I was creating my Gantt chart the dates kept changing and making my project duration a lot longer that what it was realistically. In order to fix this I used mainly my own initiative to work out how to change this. I also asked my subject teacher to help me correct and make the changes that I needed to make. All i had to do was click the tab at the top of the column which I wanted to change, then highlight the particular task I wanted to alter. Once this was highlighted, all I had to do was change the figures in the 'end date' column. I did also use the Internet for assisstance with this.