One simple way of doing it, if you haven't got too many fields, is to Set Variables for each field in the Leads table you want to copy over.
Then Go To Layout Quotes.
Create new record.
Set Fields with all the variables you have.
Set Variable [ $ID ; Leads::Ref ]
Set Variable [ $Contact ; Leads::ContactID ]
Set Variable [ $Notes ; Leads::Notes ]
Set Variable [ $LeadSource ; Leads::LeadSource ]
Go to Layout [ "Quotes" (Quotes) ]
Set Field [ Quotes::fk_LeadID ; $ID ]
Set Field [ Quotes::ContactID ; $Contact ]
Set Field [ Quotes::Notes ; $Notes ]
Set Field [ Quotes::LeadSource ; $LeadSource ]
Also, I'd nearly always use the Set Field instead of Insert Text script step
But you really don't need to copy any data over beyond that of a contact ID. If you link your records by contact ID, once you have the value for contact ID in your Quotes field you can just add any fields you want from your leads table.
See this thread for a discussion of two methods for doing what you want. One copies over the data, one links to it. Neither require a script: Auto Fill