Sounds like you didn't use a block while block sanding. Get yourself one of those Dura block sanding kits and use them for all sanding. It's the only way to make sure everything is straight. I always sand from different angles, just make sure the block is long enough to contact straight metal outside of the dent area as that is what guides the block. Then use a 2k primer (or whatever is recommended on the filler) over the filler and sand that again with a guide coat.

It takes a lot of time and patience. I've had to re-sand spots 4 or 5 times before it was perfect.

Good luck.

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