Don't torture yourself about it.
Prison time for this sort of offence *is* a possibility.
However, your Solicitor is in a better place than us being in possession of all the facts, statements and evidence.
Your contrition seems genuine and if your demeanour matches and is accepted by the Prosecutors you will probably receive a fine.
If he is laid back about it, I'd suggest that you follow his lead.
Some light-reading for you:
///Actual Bodily Harm (ABH)
What is Actual Bodily Harm?
Assault causing actual bodily harm (ABH) is a criminal offence under Section 47 of the Offences Against the Person Act. ABH involves assault or battery causing actual physical harm to the victim. The harm does not have to be serious, but must involve more than a shove to sustain a charge of ABH. Harm such as bruises, scratches and bite marks is sufficient.
ABH only requires an intention to apply unlawful force to someone, not an intention to cause actual bodily harm. For instance, if someone pushes the victim who then hits his head against a wall, he will have intended to apply unlawful force and could be charged with ABH – even if he did not intend the victim to hurt their head.
Will there be a prison sentence?
ABH carries a maximum sentence of five years and or a fine (depending on the seriousness of the offence).
For a first offence, a fine and or community order may be imposed. If the offender has previous convictions or if there are aggravating factors, a prison sentence is more likely.///