Any advice welcome! Can’t work this one out!

My little girl has been showing signs of readiness for a couple of months so we started potty training 3 days ago. On day 2 she started telling me when she needed to go but then when she’s on the potty/toilet she can’t seem to release. She then comes off but you can tell she still needs to go as she’s holding down there and keeps saying potty or toilet etc. we could be back and forth on potty for over an hour! Then it gets to a point she can no longer hold it and it just comes out wherever she is standing so I quickly get a potty underneath her. We’ve tried water play, blowing bubbles through a straw, singing songs, games, books. So many different things to help her release those muscles but now I’m not sure what to try!? Has anyone else had this issue? I’m so proud she knows when she needs to go and I thought that would be the biggest issue but it’s actually releasing the wee!