Can I ride a big bike?
There are a few things you can do. I would be very surprised if the XL is that much too large it cannot be setup to be ridden by you reasonably comfortably, if not ideally. A bike that is too large may make some technical trails a bit more challenging, so how successful you are on that bike will depend on the type of trails you ride and what you expect to be able to achieve.  

Aim here is to reduce the effective top tube length. Here a few $0 Cost, completely reversible things you can try.


Move the seat forward on the rails. 
'Slam' the stem - put the stem on the steerer first and put the
spacers on top (can arrange stem and spacers any way you like). 
If riser bars rotate the bars a little. 
If really wide bars, as is popular these days, move the controls and grips inboard. This narrower position effectively 'lengthens' your arms. 


Other things that might help if the above fails that cost a bit, but not a lot of money.
 - Flatter bars
 - Higher bars
 - Shorter stem 
 - Longer seat

If the seat won't go low enough, trimming the seat post will help. If you find a position that works, you may consider trimming the bars or replacing with narrower ones. I would hesitate to recommend trimming the steerer as unlike bars and seat posts (which can be relatively cheap to replace), The forks are an expensive bit of kit. 

Personally I suggest play with the above setups, get the bike as comfortable as you can. If you find after a few months its limiting your riding, it probably best to sell it and book this one up to experience. A bike that does not fit well is never a bargain.