Thanks for your question
You should have declared the gross amount paid - so daily rate plus expenses and then claimed the expenses arises, to form a true net position.
However, as the end result is the same, there maybe is no harm done, unless you should be registered for VAT, and then this does make a huge difference, as the need to be VAT registered is based on your turnover, so you should consider whether this would put you above £77,000
But I would from now on do it the correct way.And is VAT is an issue, then you will need to rectify this, and your self assessment income and expenditure.
I also have a small concern that as you seem to just work for one contractor that maybe you should have been paid as an employee and not under CIS. But if you have satisfied yourself that you are in fact self employed, and feel sure that this status is correct, inspite of this factor, then all you need to do is address the VAT issue and make sure you declare the income and expenditure correctly from now on.
I have added a link here from the Business Link website - (affiliated now with HMRC) that addresses the issue of whether you should be CIS or PAYE.