You're fine.  If you really want an inside look at how withholding is calculated, look at IRS publication 15-A, it's a good education (starting on page 25).  https://www.irs.gov/pub/irs-pdf/p15a.pdf

Basically, by selecting one exemption, you are saying that the first $77.90 + $43 of your weekly paycheck is tax free.  That adds up to $6286 per year, and it is not a coincidence that equals the standard deduction of $6300, the amount of income that is tax free for every single person.  In weeks when you make more than that, you will be charged 10% (the lowest tax rate) on the amount over.  In other words, the tax tables work by "annualizing" your income each week and figuring out what tax you would owe if that was your pay for the whole year.  

It should work out pretty close for most people.

If you want to claim 0 allowances, you would have more withheld but would then get it back as a refund if it was more than your eventual tax owed.

Even if you have too little taken out of your check, you won't owe an extra penalty since this is your first year of filing a tax return.

You may want to check with your state and see if they have a separate state withholding form.  New York does, and a young single person who is also their parent's dependent needs to claim Single with one allowance on the Federal W-4 but single with zero allowances on the corresponding state form, because NY tax laws treat the exemptions a little differently.  But I don't know about Oregon.