When i convert a quote to an invoice the invoice looks totally different to my default invoice. Is there a way to have the converted look the same as my default invoice?

Yes, @accounts-fixedon, there is. 

We can do this by using the Customise button in QuickBooks Online (QBO). When you convert a Quote to an Invoice, the appearance of the converted Invoice will depend on the template you choose to use. Make sure to select the default template before saving the changes. See the screenshot below for visual reference:
 

Once selected, click on Print or Preview to see if the changes reflect. The same goes when choosing a template for the converted Quote.

You may visit this article to learn how to personalise and add specific info to your sales forms: Customise invoices, quotes, and sales receipts in QuickBooks Online.

I'm all ears if you require additional assistance or have other concerns about converting a quote to an invoice. Simply comment below and I'll surely get back.