In order to align the controls in 'Nintex Form', select the control by using the mouse and move it with the help of mouse or keyboard 'Arrow' controls (up/down,right,left). And you can see 'Preview' option before publishing the form.
And you can create a SharePoint list column of type 'Currency' like below to allow only numbers and 2 decimal places.
If you need to center the input for a field (move it from the top) you will need to change the CSS Class. When you click on the field in the ribbon on the top you will see a box for formatting which will have the CSS Class. Add this in the box and it will center it for you:
For a label: nf-form-label nf-section
For a field: nf-form-input nf-section