HI will it be possible to make a mould of this part in one piece or will there be a risk of it locking?

Difficult to properly judge without seeing the side profile, but if there are any areas that undercut at the sides, then there is a risk. However, it's likely that the original panel was made in one piece. You could likely get away with a slight undercut along one side if the part is flexible. though

Try to imaging the part upside down in the mould and look for any areas that might lock themselves in

Gelcoat is a great surface from which to pull a mould, so you shouldn't have any issues with it as long as it's well prepared with a suitable release agent