Took a look at this.
Found the "Test Trials" sheet that looks like the one in your screen shots.
You have that sheet set to "Entire view". That tells Tableau to resize stuff to get the entire sheet to fit into the defined window. Change that to "Standard". Now you get fixed sized marks, and a scroll bar.
Screen shot shows you where to set that. You can set it at the dashboard level and at the sheet level.
timelines example A.twbx 636.5 KB
You can select "Show Empty Columns" option from Analysis > Table Layout menu. This will help you retain the shape of bar chart even if you filter the values. Hope this helps.