Just do the best you can with the amount of time you have. If you have very limited experience with the game engine you're using, then now would be a good time to get practicing and refining your skills. I recommend watching a couple of tutorials and looking up anything you don't know how to do, try and mix and match tutorials to achieve the effects you want, along with experimenting with other aspects of the engine. You could also set up a team with developers and designers who have the skills you don't currently have and who would like to help you make your game. But the most important thing is to have fun while making your game.