Help 2007/8 tax return...

mr_xyz_2

Got myself in a muddle. Registered several years ago as part time self employed (ebay trading) whilst holding a full time job (PAYE). Ebay trading ended Dec 2007. Started another part time business Feb 08, just weekend work basically clearing the advertising costs. Total profits for Feb, Mar, Apr 08 in region of £600. I submitted my self assesment return on line last week without including my new part time job as I was under the impression next years return could accomodate this throught the 'accounting period'. As of 2009 I am now full time self employed with this job, so expected to get a accountant to do next return and adjustments.
I,m now not to sure this was the right thing to do. I'm still registered as self employed and pay Class 4 NI's. Did this (small amount) need to be included in 2007/8's return or can it be left till next year. I see there's a facility to amend your return, can that include submitting an extra self employment form? Is this going to bring me a whole lot of hassel...
the days are counting down fast now!!!
Thanks for any help...