Ford fiesta temperature gauge

So I recently noticed that my coolant fluid was very low so I topped this up 2 days ago. However I'm struggling to suss out the temperature gauge. I'm sure that normally when I switch on my car, the guage instantly goes to the halfway mark. But at the moment it seems to be taking a while to get up to this point. Can someone tell me if I'm tripping and is it normal for the engine to take a bit of driving to heat up? Or should I be worried?

So you've been driving around without any coolant.
So now you've topped up the radiator your cooling system is working correctly. From cold an engine should take a few minutes to reach normal operating temperature.
So check the coolant level again to see if it's gone down and top up if necessary.

No your not "tripping", although I might not mind if I was LOL. No your car can take up to 15 minutes to reach normal operating temp. So don't let it freak you out. Also have you checked your water level in the Engine Compartment? If it's full, and it's not leaking you have it made in the shade. CHECK EVERYTHING UNDER THE HOOD, to make sure everything is topped off.

Surprisingly, you never noticed before that it goes up slowly from cold. But if you had already driven it it would go up immediately because it is warm. It is measuring the engine temperature.

You are not tripping the gauge, ALWAYS starts out cold and goes up in 5-10 minutes of driving.
You should be a bit worried about the coolant loss and if you "space out" the coolant and forget to check it
you will end up "freaking out" when you cook your engine.

You think the instant you start your engine it's right up to temperature? It isn't. Give it a few miles.

Yes, you are tripping, it does take a few minutes for the engine to heat up, your temp gauge is actually reading the temperature of the coolant. Don't worry, you are fine.

It can't heat up instantly, it always takes about 10 minutes

" I'm sure that normally when I switch on my car, the guage instantly goes to the halfway mark."

A normally functioning car will take 5-10 minutes to reach normal operating temperature. The temperature guage does not go to half-way the second you start the car. The oil pressure gauge will though.

"Can someone tell me if I'm tripping and is it normal for the engine to take a bit of driving to heat up? "

You're tripping and/or don't know much about the typical operation of liquid cooled combustion engines.

It always takes some time to get a engine warmed up. A few miles at least.

Look for a P0128 code if the thermostat is sticking open, this will cause the engine to run cooler then intended.
The gauge sender may be bad for the dash gauge, the engine usually has several thermal sensors so search your model for engine locations. They sell very inexpensive IR thermal guns for $20 or so, point one at the engine head and thermostat housing to see the real engine temperature when the engine is hot, then go for the dash gauge sender usually mounted in the intake manifold or engine head. When the engine doesn't seal up the pressure cap, fluid can evaporate quickly, make sure the cooling system is sealing to hold pressure when hot by feeling the upper hose quickly using a rag so you don't burn yourself. Sticky engine thermostats usually act up in cold weather, sticking open too far and not allowing the engine to reach full warmup temperature.

Low on the coolant expansion tank is no big deal if it was only a quart low, as long as there was still some in the tank.