Unlikely to be any valve damage as the 1.0 litre FIRE engine is 'fail safe', meaning that if the cambelt snaps then the valves won't hit the pistons.
To change the head gasket would have meant removing the cambelt, distributor and possibly the inlet and exhaust manifold.
If the engine turns over, petrol flows and there is a spark then it sounds like either valve timing (cambelt), ignition timing (distributor) or possibly an air leak somewhere.
Make sure the cambelt timing is set properly, then check the ignition timing. Thing is, the ignition timing needs to be set dynamicaly, meaning it needs to be done with the engine running and with a timing light. It can be set staticaly, but I'm not 100% sure how. I think you align the rotor arm on the distributor to point to a mark on the distributor housing when the crankshaft timing marks are aligned.
You can find the crankshaft timing marks and also the flywheel marks by removing the square plastic plug on top of the gearbox bellhousing near where it joins the engine.
Also make sure the distributor was fitted correctly, as I think it's possible to fit it 180 degrees out.
As Luke1985 mentioned, you can download the Haynes manual in a PDF file which will have all the information needed.
Check as well that all the vacuum side of the engine is correctly connected and not leaking. Even something simple like the vacuum pipe from distributor to carburetor can cause the engine to not run properly and may cause poor starting. If you removed the intake manifold make sure it is tightened to the correct torque settings and with a new gasket.
Other than that, just make sure that everything that was disconnected when removing the head is reconnected correctly!
Best of luck,
Chas