Continue to hold on aim as the crossbow surges, this 'follow through' is critical. For match bows, you may need to shoot as the sights 'sway' across the target. Match bows are very heavy and carry balance weights. However they also have relatively light triggers and so you can 'pull' at the critical instant rather than use the 'squeeze while holding at aim' technique I have suggested. If you want something powerful, buy a shotgun.
Crossbows are just another form of bow, very popular in medieval times in Northern Europe.
They are not as powerful as a modern compound hand bow and repeatedly proved less lethal than the traditional yew longbow on medieval battlefields. If, however, you want an accurate target bow for a quiet afternoon sticking needles in a target, then they are great fun. With a lot of practice, you can rival the scores of the big 'power' compound longbows on an NFAS field archery course, and it can cost a lot less.