Thanks for your question. The URL you have constructed is correct; if you have the unique gene ID and other parameters specified in your URL, only one result should open in the browser. Try this query on your mirror to see what might be happening:
mysql --user=genomep --password --host=genome-mysql.cse.ucsc.edu -A -e 'select count(*) from trackDb;' hg38
Enter password: (enter your password)
Let us know if you are still experiencing difficulties.