Sadly, there's not much that can be done retrospectively, so I'd definitely recommend seeing an account asap. When your income hits higher rate, you have to plan ahead to minimise tax. It's a nice problem to have. If you're only actually making £325 (£195 - pre-tax) out of a £600 gig, then it might also be worth looking at the costs/overheads of your business as that'd give you more to take home. I know mine are nowhere near the 45% mark.
Having said that, on paper, they're more like 60%! But a very significant proportion of those are money that would be spent anyway - i.e allowance for home office, telephone(s), broadband, mileage, etc and not costs that would go away if I wasn't DJ'ing.
Probably worth taking time out to reflect....
Julian