Need to respond to recruiter by tomorrow (given only two days!), have potential better offer, what do I do...

Hello,

I received an offer yesterday for a summer internship that I have decided I would most likely take. However, the recruiter contacted me today asking me to respond by tomorrow (since the manager wants to keep other candidates in case or something).

The issue is that I'm currently completing an unpaid internship at a much better company (more pay, more benefits, bigger company name and better position)... They aren't able to let me me know whether or not I would be able to continue paid work over summer until Friday, however.

Is it okay to ask the recruiter for an extension until Friday, say at 2PM, for the initial offer? What should I do? Please I'm very lost and super stressed...