of 2.7 x 2.4 does not cause any problem.It is an incidental finding.I have seen these type of cysts in very large number of patients without any problem.
Your back ache may be due to musculo skeletal pain.
Please take skeletal muscle relaxant
and B complex with antioxidant tablet.
Everything will be alright.
No further tests are needed
Nothing to worry
Wish you good health