You "believe" it is a 200 amp panel?
Is it actually a "fuse" panel or is it a breaker panel?
Is there a master breaker that would shut off all the power going out of the panel with one motion of your hand? Is that marked 200 amp?
How many breakers are in your panel? What brand is it?
Most breakers are 1" wide. Most two pole breakers for 240v circuits are 2" wide.
Most makes of breakers are available in "tandem" breakers. As an example, two 20 amp single circuits that will fit in a 1" space.
There are "triplex" breakers among some brands. If you had, say, two 20 amp circuits with 1" breakers, you might be able to buy a triplex that has a 50 amp in the middle with two 20 amp on either side, all of it being 2" wide. You could replace the former with the latter and not need to add a panel. If the two 20 amp breakers share a neutral, you should buy a duplex two pole. That is, 50 amp two pole, linked, in the middle, and 20 amp, two pole, linked, flanking it on either side.
It is not as easy as it might seem. If you do not understand what a three wire circuit is, you really should back off and call an electrician.