You might be running into the issue of your SnapWidget looking perfect in your editor, but not in your preview or live site.
To adjust the size and display of your Instagram widget:
First, click the IG widget to select it, then you will need to click into the embed code for the widget under the embed code tab in the Properties Panel. Locate the Width and Height settings there an take note of those values.
(for larger image: Right Click>Open Image in New Tab)
Next, double click the embed box to pull up the code editor. In there, you'll find the Width and Height settings within the code. Those numbers will need to be changed to match those of the Showit element that were identified in the previous step:
Then publish or preview! Your Instagram widget should be sized just like it is in the preview. If the sizing looks better but it is not centered on the page as it appears in the editor, ensure that there is no edge locking applied to the embedded element.