Just got into a company as a fresher. Have never liked doing frontend (no offence). They are making me do frontend. Now, I'll forever bear the tag of a frontend developer. Can't quit due to money issues. Don't know where life will take me.

Step 1. Learn frontend
Step 2. Maintain working knowledge of backend
Step 3. Put full stack developer on resume.
Step 4. Profit.

Some concepts you learn as frontend you can apply to backend and vice-versa, and it's never bad to learn new things

Don't give up, be proactive, look for ways to engage in backend stuff, name yourself 'fullstack' as stated earlier.
I was php+html5. Now i'm java+who knows what. Last week I digged into Jenkins and Docker. Because I could explain why I need this and what's the profit for company.

I didnt like frontend either (css 😭) but when the new css techniques came (flexbox, flex grid) it bece bearable. Especially when real frontenders come up to you to ask how something CSS related works.

I can now call myself fullstack like @padsjt said.

I still prefer backend but I dont mind doing frontend. As long as I dont have to support browsers that dont support flexbox.