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Setting the height of the form would be from your embed code but setting the width can be done in form builder.
Once you have widen your form you can shrink your field to make the field align horizontally. Here's a sample form: http://form.jotformpro.com/form/40433681260953
By default the field occupies the whole width of the form:
After shrinking the field it will be now aligned horizontally.
Kindly try my suggestion above and let me know if you have other questions.