Hello HCM user,
Me too think its just a sprain
as, you are just new to trampoline and your legs are not elastic enough to adjust with new stretch exercise.
You are advised to take few days rest and take some pain killers to ease your pain.
You can start after few days, but start with less vigorous jumping for few days than gradually increase the frequency.
hope my info helped you
Dr Hari Om Chandrakar