|I don't know how long ago you made the marmalade, but give it a while. Some jams, jellies, marmalades, etc. may take several weeks to set. If it doesn't set, you can remake it. I am also giving you the information from MSUE on testing for doneness in jellies:
Three methods that may be used for testing doneness of
jelly made at home are described below. Of these, the
temperature test probably is the most dependable.
TEMPERATURE TEST: Before cooking the jelly, take the
temperature of boiling water with a jelly, candy or
deep-fat thermometer (212 degrees Fahrenheit at sea
level). Cook the jelly mixture to a temperature 8 degrees
Fahrenheit higher than the boiling point of water. At that
point, the concentration of sugar will be such that the
mixture should form a satisfactory gel.
Because the boiling point at a given altitude may
change with different atmospheric conditions, the
temperature of boiling water should be checked shortly
before the jelly is to be made. The bulb of the
thermometer must be completely covered with jelly and not
touching the pan.
SPOON OR SHEET TEST: Dip a cool metal spoon in the
boiling jelly mixture. Then raise it at least a foot
above the kettle, out of the steam, and turn the spoon so
the syrup runs off the side. If the syrup forms two drops
that flow together and fall off the spoon as one sheet,
the jelly should be done.
REFRIGERATOR TEST: Remove the jam mixture from the heat.
Pour a small amount of boiling jam on a cold plate and put
it in the freezing compartment of a refrigerator for a few
minutes. If the mixture gels, it is ready to fill.
REMAKING SOFT JELLIES
Measure jelly to be recooked. Work with no more than 4
to 6 cups at a time.
To remake with powdered pectin: For each quart of
jelly, mix l/4 cup sugar, l/2 cup water, 2 tablespoons
bottled lemon juice, and 4 teaspoons powdered pectin. Bring
to a boil while stirring. Add jelly and bring to a rolling
boil over high heat, stirring constantly. Boil hard l/2
minute. Remove from heat, quickly skim foam off jelly, and
fill hot, sterile jars (see directions below for sterilizing
jars), leaving l/4-inch headspace. Adjust new lids and
To remake with liquid pectin: For each quart of jelly,
measure 3/4 cup sugar, 2 tablespoons bottled lemon juice,
and 2 tablespoons liquid pectin. Bring jelly only to boil
over high heat, while stirring. Remove from heat and
quickly add the sugar, lemon juice, and pectin. Bring to a
full rolling boil, stirring constantly. Boil hard for l
minute. Quickly skim off foam and fill hot sterile jars,
leaving l/4-inch headspace. Adjust new lids and process.
To remake without added pectin: For each quart of
jelly, add 2 tablespoons bottled lemon juice. Heat to
boiling and boil for 3 to 4 minutes. Use one of the tests
described under "Standard or long-boil jelly" to determine
jelly doneness. Remove from heat, quickly skim off foam,
and fill hot, sterile jars, leaving l/4-inch headspace.
Adjust new lids and process.
Sterilization of Empty Jars
To sterilize empty jars, place them right side up on
the rack in a boiling-water canner. Fill the canner and
jars with hot (not boiling) water to 1 inch above the tops
of the jars. Boil 10 minutes at altitudes of less than
1,000 feet. At higher elevations, boil 1 additional
minutefor each additional 1,000 feet elevation. Remove and
drain hot sterilized jars one at a time as filled.
RECOMMENDED PROCESS TIME FOR REMADE SOFT JELLIES
IN A BOILING-WATER CANNER
5 minutes, increase processing time for your altitude, if needed.