Your information is clear enough but also baffling because I can’t find a townland near Magilligan called Ballynascreen. The RC parish that includes Magilligan is called Tamlaghtard and includes the civil parishes of Magilligan, Dunboe and Aghanloo. None of them has a townland called Ballynascreen, and indeed there isn’t one anywhere in Co. Derry, though there is a parish Ballynascreen, but that’s miles from Magilligan).
As you say tradition, was to marry in the bride’s church so that could mean the husband lived some distance away, but James’ birth is also recorded in Magilligan, in the same location. So that makes me think Ballynascreen must be a local name. But it’s not one I can find any references to on sites like Placenames NI or from Google.
Some townland names have fallen into disuse and sometimes the records contain a local name for a smaller part of a townland, so these could be explanations but neither helps locate the actual place.
I had a look to see if I could find any trees on Ancestry with Patrick, Elizabeth & Jane but without success. The fact that there are no other children born in Magilligan after James could suggest the family had left the area. But that’s speculation.
I searched the 1831 census for the civil parishes and found the following James McLoughlins in the area:
http://www.census.nationalarchives.ie/pages/1831/Londonderry/Kennaught/Tamlaghtarde/Ballymulholland/14/
http://www.census.nationalarchives.ie/pages/1831/Londonderry/Kenaught/Tamlaghtarde/Duncrun/23/
http://www.census.nationalarchives.ie/pages/1831/Londonderry/Kennaught/Tamlaghtarde/Ballymulholland/7/
http://www.census.nationalarchives.ie/pages/1831/Londonderry/Kennaught/Tamlaghtarde/Claggan/6/
http://www.census.nationalarchives.ie/pages/1831/Londonderry/Coleraine/Dunboe/Burrianbed/4/
No easy way of knowing which was the witness to the 1836 marriage.
As far as determining whether this James is your family, you have said it’s the only one that you can find in the records that fits. You need to bear in mind that not all RC parishes in the county have records for the 1830s, so what’s on-line isn’t a comprehensive record of all possible births. For example, the next parish south from Magilligan is Limavady and they have no records before 1855. Going east it’s Coleraine and their records start in 1843. I have attached a link to a map of the RC parishes in Co. Derry and if you click on each parish you can see what records exist and where they can be found. (I think there’s only about 4 parishes in the county that have records for the 1830s).
https://www.johngrenham.com/browse/counties/rcmaps/derryrc.php#maps/