You can use ionic CSS utilities to align the center by applying an attribute text-centerto the parent element of the one you want to center horizontally.
Here is an example:
<ion-content text-center>
<img src="assets/imgs/logo.png" width="128" />
</ion-content>
In your case, I would wrap it <img>in <div>so that it only affects the image, not the elements <p>.
Like this:
<ion-content padding>
<p>Some text here....</p>
<p>Some other text here...</p>
<div text-center>
<ion-img width="180" height="180" src="assets/images/goal.jpg"></ion-img>
</div>
<p>bottom text here...</p>
</ion-content>