Help appreciated please

I haven’t knitted for yrs & recently taken back up - I’m a little confused re:Inc on sleeves (40 sts) says Inc and work into part 2 sts each end on 5th and every 12th row until 54 sts – does that mean 5th and 12th and then every 12th after that because tried that and sleeve was sooo long so unpulled so any help would be appreciated. Thank you

The numbers given don’t seem to add up to me.
Inc 2 stitches each end of the given rows is total 4 each increase row
40 sts
5th row 44 sts
12th row 48 sts
24th row 52 sts
(And if you continue, 36th row 56 sts)
Have you checked you selected the correct numbers for the size you are making as I’d expect the instruction to add up to 54 somewhere.
Maybe an error in the pattern?
Or else 36th row will have 2 increases at one end to get to 54 sts, but this could be where you’ve ended up with more length than wanted.

If you did a gauge swatch you can work out how many rows you would need for the length of the sleeve needed. This is a good way to check you are going to end up with the kind of length you’d expect for the size. If you didn’t make a gauge swatch you could make one now. I’ve had a few times when it has been very useful for me to know so many rows equals 10cm and therefore work out how many rows I need for the length I want.

You could also check with the pattern after this part to see if you should have 52 or 54… and if needed put the extra 2 stitches increase earlier than 36th row to keep the sleeve shorter.

Maybe have a look at what happens to these 52 or 54 stitches later on in the pattern to see if you can spot an error?
You can come back for advice for reaching the length you want if you need to.

Sorry, not a clear answer but these are the things I would check.
Perhaps someone else has more ideas.