Yes, try it! You will likely burn some components. Once you see smoke, turn off power, and figure out what parts are smoking, and why. Then replace those parts, make appropriate changes to the circuit, and try again. That is the only way to learn! And, yes, it costs some money in components. That's the (very low) cost of learning. I always buy three of anything; I'll burn the first one; I'll use the second one, and the third one is a spare for unexpected accidents.
Btw: For switching power, you want to use a MOSFET, not a BJT. (BJT is the "normal" kind of transistor you're currently using.) BJTs suck current all the time while they are on. MOSFETs only suck current for a short while while they switch state (to on, or to off.) A 555 might be able to drive the gate of a MOSFET fast enough to make the MOSFET and 555 survive, as long as the duty cycle is OK (say, 200-400 Hz PWM.) A 555 will not be able to drive the base of a power BJT with a hFE of 10 to get to 3A. The hFE means that you need to put 300 mA through the base to get 3A through the collector/emitter.