My first year here, I went through the same thing as you - I'd filled out everything online and only at the end did it tell me it couldn't finished.
Now, I download the forms directly from the IRS website, fill them out on the computer, print them out and send them off in the normal post. Besides postage, it's all free.
I always save the finished form and print out a copy for myself so I can use it as a cheat sheet for next year's taxes (all that changes year to year for me is my income and address if we've moved). Saving a copy on your taxes for your own records will make your life so much easier when you can use it as a guide next year.
I also have a sheet with step-by-step notes for filling out my taxes (which forms, how the IRS wants GBP converted to dollars, where to send the forms, etc).
That first year is such a pain. Just know it gets easier.
My first year here, DH and I took a full weekend figuring out which forms I needed, then going through them and trying to decode each part. I was totally overwhelmed and put it off until late May.
This year it only took me about an hour to fill them out (with DH double checking against last year's return) and I sent them off two weeks ago.