Underdone fruitcake

Unfortunately, re-baking is not going to save your fruitcakes. Before you waste more alcohol on them, cut one straight down the middle. If there is clearly a more dense (or gooey) center, you will not be able to salvage them. Fruitcakes are often quite dense, so make your judgement according to how the center looks, compared to the outer edges. Take a slug of said liquor, and try again, if necessary!

Undercooked fruitcake

Undercooked fruitcake cannot be re-cooked. It can be used as the basis of mini Christmas Puddings - a lot like a truffle recipe:

TINY BITE SIZE CHRISTMAS PUDDINGS
1 fruitcake [800 g/28 oz]
8 oz dark chocolate chips [semi-sweet]
4 oz butter
2 tablespoons of Rum or Grand Marnier or Brandy or orange juice [which ever]
Extra fruit or citrus peel (optional)
Icing / Decoration
White Glace Icing (1 cup powdered sugar mixed with 1 Tbsp water) OR
8 oz dark chocolate, melted
Silver Cachous or Glace Cherries
THESE ARE BEST MADE 1 - 2 DAYS IN ADVANCE TO ALLOW THE FLAVOURS TO DEVELOP. STORE IN THE REFRIGERATOR.
Melt the butter and chocolate together in a bowl over very hot water. Once it is melted, stir well. While it is melting, crumble the fruit cake into a separate large bowl. Add the Rum / Grand Marnier / Brandy / orange juice and mix it through. Add the chocolate mixture and mix well until it is all combined. Line two large baking trays with greaseproof paper. Take one teaspoon of the mixture and roll into a ball, place on trays and continue until you have used up all the mixture. This size will make between 70 and 80 tiny Christmas puddings. Alternatively, divide the mixture into a dozen and make 12 larger puddings [a set of muffin tins as a mould works well]. Put the trays into the refrigerator for 1-2 hours to allow them to set. Drizzle icing or chocolate over the puddings, allowing it to trickle down the sides. Put a small piece of glace cherry or a silver cachou on top of each one and return to the refrigerator to set.

Gooey

How gooey is gooey?

Is it goo from the top [centre] crust down to the base [centre]?

If it is too wet, then scrap it away and use the rest: but, just remember that unbaked cake batter is eaten by cooks and kids the world over, every day....Fill the depression with fruits, edible flowers, nuts, or sweets [candies]

If the cake is round, then cut a neat circle in the centre to remove the soggy bit. Fill the centre with glacee [ candied - crystalline] fruits and glaze the fruitcake top with strained, boiled down jam [jelly] eg apricot.

If the cake is square, you can still do the same: place a cake stand [skinny one] in the hole, and pile it high with fresh fruits, misc. nuts, or sweets [candies].

Cut the cake down the centre and portion one half: leave the other half in one piece. If the cake is not completely eaten, then the half, can be store or frozen in a single piece. Don't cut it all up, unless it is required.

The trick of handling mistakes, errors, problems and "flops" is to innovate and create: the cake was MEANT to
1. have a hole in the centre
2. have fruit/sweets all over it
3. be the base of mini puddings

Never admit defeat - create!

My fruitcake recipe calls for baking in a 275F oven for a much longer time depending upon the size of the pan. I always worried about my cake being underdone until I found a suggestion to use a meat thermometer to check the internal temperature. The recommendations ranged from 195F to 210F. Perhaps this will help for the next time.