Vous utilisez des backticks [utilisés pour les colonnes ] pour les variables. Utilisez des guillemets simples. Essayez le code ci-dessous
$sql="INSERT INTO registration (enrollno, fname, lname, fathername, coursename, yearsem, facultyno, hostel, roomno, email, mobileno, peradd, district, state, amount, pwd, tnc) VALUES ('$enrollno','$fname','$lname','$fathername','$coursename','$yearsem','$facultyno','$hostel','$roomno','$email','$mobileno','$peradd','$district','$state','$amount','$pwd','$tnc')";
