Changed some parts but still have a question

I changed thermostat, added stop leak to oil, put fuel injector cleaner in gas, put coolant in radiator and reserve tank, changed air filter, hesitation seemed to end, but after driving about three miles home and letting car cool, radiator was lower on coolant than when I put it in, and reserve was fuller! I will be replacing the cylinder gasket, spark plug wires this week, there are two bolts missing off the cylinder head, bolt 2and 4 going from the left to right, not sure if that's has anything to do with anything! Don't find coolant on ground ever and when car is hot don't see it spraying anywhere! Yet when I drove the three miles gauge went to half way between h and c but bobbed up to 3/4 towards h a couple times but then back to half! Is this an issue I have to readdress or faulty temp gauge needle! I am doing the work myself as much as I can because I am basically broke! Please you can text me with advice also 248-892-0267, thanks again, Gail