Make sure you do the motion properly, people including myself often tend to get sloppy on the second quartercircle.
Make absolutely sure that you hit the punch button right after the forward input.
Record your training room session and upload it to youtube and I can show you exactly what goes wrong.
You had trouble doing multiple hadokens in a row as well, so I am going to assume that you don’t do the hadoken motion cleanly if you do it a couple of times in a row.
When you have trouble, slow it down, if you don’t see progress after half an hour, quit do it for half an hour again the next day or a couple of hours later if you got time.
You can slow the motion down to the point where it doesn’t come out, just make sure you do it properly and speed it up slowly.
It all comes with time eventually, just don’t expect to sit there for 15 minutes and then you can do it.
You really have to work hard for your skills in fighting games. This is not like other games where you start wrecking shit after a couple days of playing.