>>> "I've been given a section 39"
It's not clear what you mean by that. Have you been charged under Section 39 (of the Criminal Justice Act 1988) or have you accepted a caution by admitting a breach of that legislation?
'Section 39' relates to 'common assault'. It's the lowest level of assault, relating to assaults which don't cause any significant injuries. Simply pushing someone amounts to 'common assault'.
While the penalties for 'common assault' go up to 6 months imprisonment, a custodial sentence is hardly ever passed. Most Section 39 offences are either dealt with by a police caution or, if they go to court, result in a conditional discharge, a fine or possibly a community order. (I'd guess at a conditional discharge if your case goes to court). See pages 23 to 26 here to read the sentencing guidelines that magistrates work to:
https://www.sentencingcouncil.org.uk/wp-content/uploads/Assault_definitive_guideline_-_Crown_Court.pdf