This normally is a rounded bushy shrub rather than a tree shape

Unfortunately, the only pruning this shrub will tolerate is a light clipping immediately after flowering, to remove spent flowers and taking about an inch of green foliage. If it has developed a bend in the main trunk, it cannot be corrected now - major cutting into old wood may cause death.

Many thanks for your advice. I did buy it as a standard but will continue to prune as advised as it is still lovely and healthy and I get lots of flowers.