Thanks, man! I made it so you only have three bullets because it seemed too easy if you could just go all Rambo on the aliens. But I didn't know about the high score thing, thanks for telling me. It's fixed now.
I tried it out again and confirmed that the score saving is fixed. Preventing players from spamming isn't a bad idea (depending on the type of game you're doing -- look up "bullet hell"), but giving them only three bullets at a time has some problems. Mainly, it's not an intuitive mechanic. It took me a minute to figure out why shooting felt so weird. A better idea might be to have shots on a reload timer. If you do that, having a reload bar on the screen would be really useful. That way it's really easy for players to understand how the mechanics work, and you maintain your goal of preventing bullet spam.
On a side note, if you keep up with listening to player feedback, being honest about missing bugs and fixing them when people point them out, you will keep in good stead with your players.
I like that you made them go up and down; it changes things up in a fun way! The reload meter works perfectly too, it's a really intuitive system to use and I still have to time my shots. It feels like I'm playing a real arcade game now, which is pretty cool. I'll see if I can try out multiplayer with someone and post another review when I do. Good work on your first game!