Gibble, you're probably holding the Z button instead of just tapping it. Holding it brings up the whole map with the green dot, but tapping it will bring up your radar. I had the same issue at one point.
Wow! This game is awesome! I was about to pay the $7 price tag on the game's website, then I found it on here for even cheaper than that. Trust me, it's definitely worth the $5 investment. I like how you can customize your units and the sheer amount of challenges you can complete in-game. Hopefully the developer continues to add content to this game.
The first boss on hard is difficult, but if you re-spec to speed up the winged bombers a couple levels and place two thunder globes, then two freeze rays, you'll be able to keep the boss busy long enough to take him out. I was level 11 when I did it, and I had to be really tight about point distribution. Level 11 is also about as high as you can realistically hope to get in the first six levels (this includes the hidden level)
I couldn't last any longer than 360 seconds or so, then tonight I came back to it and got 660ish my first try. Try to judge which meteors are really a threat to you. If they don't look like they'll hit you, don't shoot at them, and aim for the sides of the other meteors. If you get any "ally" turrets, this becomes a lot more complicated, and as someone else said, they're more of a hindrance than anything.
 "Decision:Medieval"){kind=icon}
 "Boss Slayer"){kind=icon}
 "Defender's Quest (lengthy!) Demo"){kind=icon}
 "Balloon Invasion"){kind=icon}
 "Balance Balls 2"){kind=icon}
 "Red"){kind=icon}