Potete correggere questo?

Hi Inna,

Thanks for writing. As an Italian mother tongue speaker, I would say like follows:

"Ho fatto ginnastica dalle nove e dieci alle dieci e mezzo"
or, as you prefer:
"Ho fatto ginnastica dalle nove e dieci alle dieci e mezza",

since in this case both 'mezzo' and 'mezza' are correct.
I would like to draw your attention to the placement of the verb. If possible, try to place the verb after the subject as written in the corrections above. Although it is not a fault to express yourself as you did (with the verb at the end of the sentence), it is however typical of spoken language or to highlight the fact that you exercised (instead of, for example, reading or listening to music).