leds and motor on small diarama
The CR2450 is rated at 620 mAh typical, but only at an average drain of less than 0.4 mA (the equivalent of a 7.5 k&Omega; load). You are attempting to draw several orders of magnitude more current than that, so it isn't surprising that you get significantly less energy out of it.

You need to pick a power source that is more appropriate for your load. Start by deciding how much power you require (LEDs plus motor) and how long you expect it to run. This gives you the total energy needed. Then find a battery that meets BOTH the power and energy requirements.