I can read music - sort of - I was taught as a child but lost it when I began playing in bands. I can read basic charts, but note durations throw me. As do notes way above or below the stave

I've downloaded BIAB songs from the internet and tried to play along, however, I have a fairly good ear for music and I tend to play what I think "should" be there, as opposed to what is really there. and once I've played it a couple of times I memorise it and I tend to ignore the dots and play what I think is right.

And when I do get a song that I don't know, I have no way of ascertaining if I'm playing it correctly.

Apart from going back to music lessons, can anyone suggest a (perhaps) a program that might assist me?
TIA

Cheers,
Keith