How can I stretch my texts

You can animate the horizontal scale of the entire text layer or use a text animator to animate the scale of each character. If you want the left edge of each letter to stay in the same place, you will have to increase the overall tracking at the start of the shot to allow each character room to move, and then you will also have to combine scale and tracking values in an expression to keep the characters from moving. 

Start by adding a Scale animator to the text layer, then fiddle with the staff and end animator properties until you get that part to look right, then add a tracking. Scale happens from the middle of each character, so you will also have to animate the X position or anchor point of the text layer as the characters change the width to keep the left edge of each letter in the middle. 

You could develop expressions to keep everything lined up or try just setting keyframes. The process is going to be a lot easier with a Monospaced font. 

The other option would be to put each character on a separate layer, Left Justified, then animate each layer's x scale property.