Trip to Rocky Mountain

I haven't been travelling much lately, largely because of my work schedule. But the most impressive trip in my life is the one when I went to Rocky mountain with some of my friends. Back then we were immature in our early twenties, immature, and unprepared for a long trip, so we even forgot to check the gas in the car before we took off. We spent the entire night in our rented car with some freight trucks around in the a rest area off the highway! But it was all still fun as we talked throughout the night. When we arrived at our destination, we were astonished by a the breathtaking scenery and pure, untouched nature. And the towns of Banff and Jasper were beautiful. It was like being in a village from a fairy tale. We had planned for a four day trip and but we were still short on time to explore everything we wanted. of the many sights things as tourists.

Notes:  

1. The verb form "been + verb + -ing" has the connotation of "over a specific period", but this period is ambiguous if you don't add one.  Also, if you want to put "largely", that is fine, but you should make sure to have a comma before you have it, because otherwise you would expect "largely" to be modifying "travelling much", not "because of my work schedule".

2. It also doesn't really make sense to use "but" after the first sentence, because the first sentence has the nuance of "a period", and the second is talking about your entire life...

a. "I haven't travelled much, largely because of my work schedule, but, out of the few trips I have gone on, the most impressive was when I went to The Rocky Mountains with some of my friends."  (This is consistently talking about your entire life.)

b. I haven't been travelling much recently, largely because of my work schedule, so I have recently been reminiscing a lot. The most memorable trip I have gone on was when I went to the Rocky Mountains with some of my friends.(here we remove the but, and so change the language.  The first sentence is now a lead in into your story.)

3. You can't say "immature in our early twenties" because immature is an adjective and you have no noun for it to modify.  If you wrote "immature (young adults/ tourists/ kids/ etc.) in our early twenties" it would make sense.

4. You already mentioned gas, so we understand that you ran out of gas.  Thus, you can just write, "we spent the entire night"