So I have been plastering for 2 years mainly onto plasterboard but yesterday I got a job to re plaster a livingroom and chimney breast, I pva'd the walls as usual waited for it to go tacky & mixed my plaster, I applied it to the wall and then trowel the rough edges instantly, I left the wall for half an hour before a dry trowel then left for 10 mins to wet trowel then the final dry trowel. My question is the plaster did not finish completely flat? Although the surface I plastered on was flat near on completely flat apart from where a cable had been embedded :/ I've never had this problem before can someone recommend a fix for this as I don't want to leave a customer with a bad finish