Allow the gel coat to fully cure, I usually leave it overnight to check that it has fully cured, touch the surface in several places paying paticular attention to the corners, it should feel tacky, that's normal, but no color should be on your finger. If there is it has not fully cured, leave it longer and don't be tempted to continue as it will react.
If all is correct, I now mix the resin for the first layer which is the tissue, this is awkward to use as it is so fine and wispy, a lot of people miss this step, not a good idea you end up with air bubbles everywhere. Tissue is used to even out the surface of the gel coat, and as it's very flexible so that it can be pushed into all the nockes and crannies that matt would not go into.
Paint the surface off the mould with the resin, lay the tissue on top and quickly and gently stipple the tissue into the resin, paying paticular attention to any sharp corners and edges. Make sure there are no air bubbles anywhere, you may find that it starts to go wispy and you start getting the same effect as you get when you put your hand on a cobweb, change brushes and go back to it with a well resin wetted brush. Get it as good as you can and leave it, it does not matter, the wisps will not affect the next layer just make sure the are no air bubbles.