Hello Ludadoo. I am a cake decorator. It's fine to ice your cake now. Do you want a few tips to start you off? Well, here's what I do. You can take it or leave it.
To prepare the cake, I trim the top so that it's flat and then turn it upside down so that the bottom becomes the top. I fill any gaps and holes with Marzipan before I start.
You need to use something as a crumb coater and to stick your marzipan on. I use Apricot Jam and heat it in the microwave for a few seconds so that it is boiling hot (this stops the cake fermenting). I brush it on and roll out the marzipan and then just smooth it on. I do it in 2 parts. First I roll out enough for the top on some icing sugar (keep lifting up to check it's not sticking and make sure you lift it as the last thing you do after you have finished rolling), then I turn the cake upside down, place it on, cut around the shape of the cake and then turn over back the right way. Make sure the sides are pushed in to be level with the cake.
If it's a round cake, I do the side in one go, measuring around the outside with a piece of string so I roll out the right lenth. I roll the piece slightly wider than needed. Use icing sugar and keep lifting up again. Stick onto the side of the cake and get a sharp knife to trim the top (cutting inwards towards the centre of the cake, not outwards). Next, make sure that the edges are fully joined at the top.
If it's a square cake, I marzipan each side individually in the same way and make sure they are all smoothed together so that there is no gap (lines don't matter becuase it's going to be covered)
I hope this helps get you started.
Happy cake decorating