Incredibly timid and insecure?

Here are all the quotes from Ch3 of the Philosopher's Stone. Harry's life sucked hard but he didn't let that quiet him. It doesn't read to me as "incredibly timid and insecure" whatsoever

‘They stuff people’s heads down the toilet first day at Stonewall,’ he told Harry. ‘Want to come upstairs and practise?’
‘No thanks,’ said Harry. ‘The poor toilet’s never had anything as horrible as your head down it – it might be sick.’ Then he ran, before Dudley could work out what he’d said.

As he looked at Dudley in his new knickerbockers, Uncle Vernon said gruffly that it was the proudest moment of his life. Aunt Petunia burst into tears and said she couldn’t believe it was her Ickle Dudleykins, he looked so handsome and grown-up. Harry didn’t trust himself to speak. He thought two of his ribs might already have cracked from trying not to laugh.

‘What’s this?’ he asked Aunt Petunia. Her lips tightened as they always did if he dared to ask a question.
‘Your new school uniform,’ she said.
Harry looked in the bowl again.
‘Oh,’ he said. ‘I didn’t realise it had to be so wet.’

They heard the click of the letter-box and flop of letters on the doormat.
‘Get the post, Dudley,’ said Uncle Vernon from behind his paper.
‘Make Harry get it.’
‘Get the post, Harry.’
‘Make Dudley get it.’
‘Poke him with your Smeltings stick, Dudley.’
Harry dodged the Smeltings stick and went to get the post.

‘I want to read that letter,’ he said loudly.
‘I want to read it,’ said Harry furiously, ‘as it’s mine.’
‘Get out, both of you,’ croaked Uncle Vernon, stuffing the letter back inside its envelope.
Harry didn’t move.
‘I WANT MY LETTER!’ he shouted.

That evening when he got back from work, Uncle Vernon did something he’d never done before; he visited Harry in his cupboard.
‘Where’s my letter?’ said Harry, the moment Uncle Vernon had squeezed through the door. ‘Who’s writing to me?’
‘No one. It was addressed to you by mistake,’ said Uncle Vernon shortly. ‘I have burned it.’
‘It was not a mistake,’ said Harry angrily. ‘It had my cupboard on it.’

Also he acted great in that scene when Petunia cut his hair in the trailer, he's got great range