Did I make a mistake in Financing? How long do you finance?

BTW, I checked with my credit union before sending double payment to make certain that any amount over the regular payment amount is in fact applied to principle...with our loan, it is. On the statement they send me every month, it shows the extra principle payment as well as how much of my regular payment was applied to interest and how much to principle. I never write 2 checks but 2 checks may be the way to go if dealing with a loan company.