I would be a little careful making fit decisions based on how the bike feels on a trainer. Every bike I have ridden on a trainer felt like it needed to have a shorter and higher stem compared to my on-road position.

Do you have another good fitting road bike to compare the top tube dimension? No need to guess about the dimensions if you have measurements to compare. If it turns out that the measurements and your feelings add up to a need for a shorter reach to the bars and you are already using a short reach stem, you still have options.
Raising the stem will shorten the effective reach a little. Shorter reach and/or narrower handlebars will definitely help.