Hi Sara, hope you're doing well! Yes, you can fix it, and no, you don't need to start again, which is always a good thing!
A couple of things to try if your ganache isn't working properly are as follows: -
If the ganache is breaking or separating then whisk in a tablespoon of warm milk or cream, keep adding a little at a time until it comes together either that or put it in the fridge and allow the cocoa butter in the chocolate to set.
If the ganache seems grainy re-heat it and start again.
If it is too thick, then place in a bowl over a simmering saucepan and mix together slowly or place in the microwave to melt. If the ganache becomes too runny, let it cool and set a little at room temperature and then put in the fridge to thicken.
Remove from the fridge allow to bring back to room temp and then whisk; this can then be piped.
Also, check your ratios of chocolate to cream if your fat to liquid quantity isn't right; this may cause the mixture to split.
Here is a ganache recipe/mini-tutorial for you.
Here is a Chocolate Ganache Tutorial:- Ingredients:- 350ml Double Cream 175g Dark Cooking Chocolate (Approx 50% Cocoa Content) 175g Milk Cooking Chocolate (Note: This recipe can be modified to suit your needs, just use the same amount of double cream to chocolate). Method: 1. Pour...
www.helpmebake.com
If you need anything else, then please let me know.