Welcome to KH!
Looks like an adorable sweater.
For the sleeves, after the cast off of 2sts at the beginning of the next 2 rows you have 44sts. Work 4 rows then dec 1 stitch at each end of the next 3 rows, call them rows 1,2 and 3.
Continue to dec 1 stitch at each end on rows 5,7,9,11,13,15,17 and 19 (that’s the 8 following alt rows). Then dec 1 stitch at each end on rows 21,21,22,23,24 and 25 (that’s the 6 following rows).
As for the direction to end after row 4 of the pattern, I almost never get row gauge so I’d say don’t worry about where you are in the stripe pattern. Just make note of where you are in the stripe pattern when you bind off the 2sts in case you have to work the same stripes on the other sleeve.
Thank you. I will try that and hopefully it will fit. What about the increasing part and that 15 rows ? I mean this is where it becomes too long I think. If I start with 42 rows , do 31 rows increases ( 1 + 1 on 10th row, +1 on 20th row +1 on 30th row) then do 15 more rows, then ,than 2 rows cast off, than 4 more rows and than 25 rows decrease, this will be waaay too long. Something is not right here.
You can always shorten the sleeve before the bind off for the underarms.
If you want to shorten the sleeve cap (the rows after the underarm bind off) you might try decreasing 2sts at the beginning of every row rather than one stitch at each end of alternate rows.
Does it look like you cast on sts after the first stripe at the beginning of that middle yellow stripe?
Its the increases there. I tried to do 3 rows of increase one after the other instead on every 10th row to shorten it, but didn’t work our and now the sleeve looks weird.TBH the increasing part is also very confusing for me. INC 1, than inc 3 foll 10th row( i understand this as inc 1 now, and 1 on the 10th row, and then 1 after another 9 rows , and 1 after 9 more. Which makes it 31 rows) after that do 15 rows straight , 2 rows with cast off,and then 4 more roll after fthe stripped pattern has finished, and makes total of 52 rows. But this makes NO SENSE AT ALL.the strip pattern is only 27 rows, and I have to start with it at the same time as the first increase and on the pattern it says the stripe pattern will end 4 rows after the 2 rows of cast off. This is all so confusing and makes no sense to me.
The “at the same time” directions mean that as you are working the 42 rows in yarn A, work the increases. Don’t wait till the 42 rows are complete before starting the increases. So change to the larger needles and on the next row, inc 1 stitch at each end of row 1 and then rows 11,21 and 31. (You had that spacing correctly done.)
After the 31 rows, work 15 rows or work to whatever length you want here and then cast off 2sts at beg of the next 2 rows. If the pattern has a schematic, it’ll give you a length for the sleeve as a guide.
As I mentioned, don’t be too concerned about the stripe and finishing it before shaping the sleeve cap. Try to line the stripe up as much as possible with the sweater front but ultimately, you don’t want the sleeve cap to be so large that it won’t fit into the armhole.
What is the name of your pattern?
Oh ,wow, that actually makes so much sense 
I never even thought of starting the increase at the beginning. I still don’t think the calculations are right to match the strip pattern, but will try it and see what happens. I can try and match it as much as possible, I just get annoyed I cannot get it right like the pattern say.
Thank you so much, will give it a go and let you know the result. The pattern is Milkeyway by Patons ,its a free download from Deramores. I can send it to you if you like.
Oh, really sweet! Enjoy finishing up.
https://knitpatons.com/en/designs-patterns/milkyway-jumper
Thanks anyway. We can always download from the site.
Thank you so much, it worked The only thing is that after the 2 cast off, start directly to decrease, without doing 4 straight rows. The 4 indicated that at the end ,there will be 4 rows left to do with colour A. Thank you again, I would not have done it without your help.Of you don’t mind , if I get stuck again to ask you? Oh and the pattern, from Patons its £1.5. From Deramores its free 
That’s looks lovely. Come back anytime. You’re a member of KnittingHelp now and we’ll be happy to see you back.