I picked up this reel last year because I thought I would start Musky fishing. I have casted it maybe 25 times.. would it be better to sell it or could I convert it for flipping/pitching?

Which model?  While I'm no Musky fishermen, if it's a 5500 series I'd think that's a little on the light side for musky fishing. 

I'm pretty sure its a 5600..

thats still a little light for musky if i was gonna get a reel for musky it would be maybe a 6500 but i have a quantum iron for flippin' and pitchin' and swimbaits and it works fine

If it's a C4 it would be 5600. C3 is 5500. Is this the reel you have posted in the flea market or another one? That one is a 5500 C3 from the pic.

This is the one I mentioned in the flea market but I did  not post a picture. It is navy and gold.

Sorry, I got the posts confused, and it's only Monday! Gonna be a long week....

thats still a little light for musky if i was gonna get a reel for musky it would be maybe a 6500 but i have a quantum iron for flippin' and pitchin' and swimbaits and it works fine

I use the same reel for musky waters when using large swimbaits for bass- Have landed musky with no problem at all. 

Abu makes a C4 in 4600 and 5600 sizes.  I have an older C4 4600 that works great for Carolina Rigging due to the fast gear ratio.  IMO, their spools are too heavy to make a good pitching reel unless you only pitch heavy jigs and plastics.  It's not that you CAN'T use them for anything, just that there are better choices.  I'd stick to throwing lures of at least 3/8 oz with one.