It is best to avoid horizontal and vertical flow in the same document. This can cause significant confusion and should be discouraged.
There are a couple solutions to avoid vertical scrolling issues, which is what you tried to avoid by having a mixed layout. I believe these solutions are better than mixing layout flow.
Use multiple steps. Have the user fill out a portion, then click Next to see the next part of the form. This is the most common method used, and has a vast body of literature supporting its ease of use. I recommend it. But...
If that is not acceptable for some reason, how about this alternative? Use a standard vertical flow to your document, but when the focus enters a new section of the form, auto-scroll the document to vertically center that section on the screen.
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No section should be taller than the expected screensize. When the user reaches the end of a section and focus enters the first control on the next part, the screen should smooth-scroll to center that part of the form. This still allows them to navigate up and down without using the scrollbar, though they still would be unable to see the entire form onscreen at once. This navigation method is related to a vertical Cover flow, but adapted to form segments.
Not that a 'form section' in this context is referring to a chunk of fields, not each individual control. 'Address', 'Personal Information', etc.