On the Button in mid stages of freeroll

I have a 2.5k chipstack in a FT freeroll, and there are 600 people left. One person calls, and everyone else folds to me (I'm on the button). Blinds are 400, and I check. Flop comes A9A. I throw out a 400 bet, other guy calls (he has 7k chips). Turn comes a 6. I bet 400 again. He calls. River comes a 3. I'm thinking he probably doesn't have an ace, so I bet 400 again. He calls, and he shows ____.

Did I play this wrong? 89 seems too weak to bet, on hindsight. Average chipstack was 8k at the time. This was a freeroll turbo.

Also, with 3k, and I'm on the button with 77 (one caller), I push all in, since there are 500 blinds. The other guy calls with ______. Is this bad? I put him on a non-pair or lower pocket pair.

First Hand:
If you were on the button you called/limped 400 - you can't check......or were you big blind (BB) ?
Min - betting the flop on that board is too weak imo (remember you are representing a set of aces)
Your betting 400 at turn and river shows no strength either - it only shows that you were unsure what to do.

I guess if you had fired 2 to 2,5 BB (800-1000) you would have made him fold (or check raise you holding Ax) on the flop and it would have been cheaper than betting 3x400=1200, too.
Remember, your bluffs and semibluffs (like here) need to tell a story that sounds valid.

Second hand:
before shoving you ought to know what you could be up against...

You'll be coinflipping against any two overcards, are dominated by higher pps and dominate lower pps.

77 can be very nice if you hit the set. If you don't and see overcards on the flop it gets very hard to keep.

There's no real need to shove 77 for you - standard raise to 1250 (2,5BB) works better here. You can still shove flop,turn or river.

Ah, wrong terminlogy. I meant Big Blind. Thanks for the critique for both hands I think for the first hand I was thinking of not needing to bet big to make an opponent fold, and I see, now that you said it, that a minimum raise where it would only cost a portion of my check was too weak.