Ol' Patchwork is going to help you not get nervous with your first game:
1. Keep a sense of what YOU the developer wants to happen in the game.
Wanna make a game about a boy who uses a magic guitar that defeats a evil wizard? Do that stuff! Here is how I would go about it story wise:
"Clappy was a spirited boy, he wanted to become the greatest musician ever, he trained his life up to the age of 14 in he sacred arts of magical music. Clappy, by chance of word of mouth by his mentor went to a shop where they sold musical instruments. Clappy asked for a instrument and the shop keeper gave him said magic guitar, "Thunder bringer". Just while playing it, The guitar chosen him to defend Station city from dark forces."
2. Don't worry about other games make THIS GAME your game.
Undertale, Deltarune, Bob's first rpg, yeah they are great games. But they aren't YOUR games. Don't let other games intimidate you, just make your own game and have fun with it. SGB can do a lot of neat stuff if you are willing to make that neat stuff happen!
3. Have Fun
If you aren't having fun with the game you are making then don't make it, goofy! Make it fun, name a item as "Enrikca!" or have a dog in your game use the power of song to defeat enemies. Have a hammer in the game that has the face of a baby and it burps up fire that burns enemies alive. It's your game, HAVE FUN.
4. Keep it simple at first then make it more complex
Keep your first game simple. Yes, you should make it good, story driven, and creative, but your first game should be easy to follow, but for now simple. Don't worry about time. Just Have fun and make your game your own creative and growing world.