Form 400 and previous taxes - help

[gadgetabc]

Hi friends. I need help filing form N400. I became a permanent resident and got my greencard on December, 15 2014. At that time I didn't meet the substantial presence test, so, in 2015 I filed my 2014 taxes using the form 1040-NR because I only lived 15 days in the US during 2014. However I'm not sure if what I did was all right.
Now I'm trying to apply for citizenship and one of the questions is if I ever filed taxes as a non resident since I've got my greencard.
Should I have filed 1040 or dual citizenship instead for 2014. Should I try amending those taxes before submitting form N-400?
Thank you so much for your advice!

[N400questions]

I don't think you can amend tax returns if they are more than 3 years old can you?
Form 1040X only lets you go back 3 years.
So I don't think you can change your 2014 taxes even if you want to.
Don't take my word on that.. call IRS.

[gadgetabc]

Yes! I don't think I'll be able to amend those taxes. I think I'll just need to explain what happened. I'm going to call the IRS tomorrow just in case.
Thank you!

[bobm445]

I don't know what the basis of your green card was but I'll use a few examples to show that you should have filed as a resident. If you got married on new years eve before midnight you would file as married for the whole year. Same as a baby born at 7PM on Dec 31st. You get credit for a dependent for the whole year. What was your status prior to the green card?