Quick Enthalpy Change Question

I'm calculating the enthalpy change of a reaction in solution.

KHCO3 (s) + HCl(aq) -> KCL (aq) + H2O (l) + CO2 (g)

Basically I used 30cm^3 of 2Mol dm^-3 HCl acid and put in 3.9g of potassium hydrogencarbonate.
I recorded the temp change, it decreased at the end of 7minutes by 7C, this would mean it is an endothermic reaction and so whatever the enthalpy change is, will be a postive number, correct?

Now that I want to work out the Heat given out by the solution, for mass do I use 30g (assuming 30cm^3 of the HCl acid is 30g) + 3.9g?
So should the mass I use to calculate the heat given out by 33.9g, or should it just be thirty?

Assuming I should use 33.9g, and knowing the spec. heat capacity is 4.2 and the temp change is -7...the heat given out should be 997J, correct?

The next bit confuses me. I am supposed to use whatever value I got for Heat given out and divide that by a concentration, so it should be
997J/2 (conc of the HCl acid) to get the enthalpy change of this reaction, right? Or have I got it wrong anywhere above?

Thx