If you are using a text app with a different number, it is unlikely that someone can find your real cell number unless you have shared it with them or they have access to your device. The text app works by assigning you a different number to use for texting and calling, and it does not reveal your real cell number to the recipient.
However, it is important to note that if you have linked your text app to your real cell number, it is possible for someone to find your real cell number by tracing the app back to your original phone number. Additionally, if you have used your real cell number to register for the text app, there is a chance that it could be linked to your account.