If you have a good lubricating lather you can overlap several times without irritation, just so long as your razor is good and sharp, and you don't apply pressure.
I can get very close on my WTG pass, but with overlap, I probably hit every hair at least twice...
There's an art to straight shaving, and we are all students. I don't care if it's shave #1 or #10,000 There is always something that you haven't tried, or mastered yet.
I remember when I started, it took me 3 months before I could get a close enough shave that I wasn't touching up with my Mach3, and another 3 months before I was confident enough to throw it away.
If you still have a disposable, don't be ashamed to clean up with it, do what you can with the straight, don't torture yourself. There is no shame in learning, and if you do it in a fashion that keeps your confidence and comfort level high, you will be successful.