Chocolate swiss roll with black cherry filling

I made this swiss roll yesterday and it was nice. But I still don't know how to roll it into perfect round shape. I need to figure it out. Can anyone help me?

Here is the recipe:

Ingredients:

5 medium size eggs
80g caster sugar (divide equally into 2 portions)
50g plain flour
50g cornflour
35g olive oil
1 tbsp cocoa powder
1 tsp instant coffee powder
1 1/2 tbsp of hot water
1/2 tsp baking powder
1/4 tsp cream of tartar

Filling:
1 can of Nestle Tip Top squirty cream
1 can of Hartley's black cherry

Method:
1. Preheat oven 175 degree. Grease and line the tray with a greaseproof paper.
2. Mix cocoa powder and instant coffee powder with hot water. Set aside.
3. Sift together plain flour, cornflour and baking powder for 2 -3 times. Set aside.
4. Separate the egg whites and egg yolks. Whisk the egg whites and cream of tartar until foamy. Add in 40g caster sugar gradually, spoonful by spoonful. Whisk till fluffy. (make sure the egg white doesn't fall out when you turn the bowl over)
5. In another mixing bowl, hand whisk the egg yolks with another 40g caster sugar. Add in olive oil. Put in flour gradually and mix well.
6. Fold in 1/3 of egg whites into egg yolks mixture lightly and gently. Repeat the rest. Lastly add in the cocoa mixture and mix well.
7. Pour the batter into baking tray and bake it at 175 degree for 15 mins.
8. Remove from oven and peel off the greaseproof paper. Leave it to cool on the rack.
9. Spread enough cream on 3/4 surface. Then top with some black cherry and roll it up.
10. Wrap it in a cling wrap and chill it in the fridge before serving.