Internship vs study for GMAT vs study abroad

I'm in a second year of my bachelor degree in a European university.

Next year (the last one) I'll spend the first semester in a university in the US for an exchange program.

I was thinking of finding an internship for this Summer, but all the good companies I applied to said that they want someone who stays for more time and I can't since I'm leaving Europe in early September.

Also, I'll be back home in March of next year and I need to apply for a master's degree in around the same period, so I would need to already have taken GMAT.

The question is: if you were me, this Summer would you try harder to find an internship even if it's not the best quality or would you focus on GMAT? I'm assuming that I wouldn't be able to take GMAT or do an internship while I'm an exchange student. Is previous work experience so important to be admitted to a top business school, or can I compensate it with high grades and international experience? Maybe I can even try to get involved with some student club while I'm in the US.

Thank you in advance for your help.