Congrats and best of luck as you make the move to college ball. Take it seriously and give it the effort and dedication it deserves, but make sure you continue to enjoy what you're doing.
Bossman's advice is spot on. Be coachable and ask for feedback...but also make sure you know how to accept feedback. You're a rookie, so nobody is expecting you to be an expert on the rules yet (though becoming a great rules guy will make you a valuable asset on a crew) or to know the college mechanics inside and out, so if someone tells you that you're doing something wrong don't feel like you have to explain or defend what you did. In fact, your mouth can get you in far more trouble than just about anything you do on the field. The old saying about the reason we're born with one mouth and two ears is legit. I could tell you a story about a guy from around here who was hired and fired within a span of a couple months because he went off to a scrimmage and couldn't accept criticism from someone directly affiliated with the supervisor without defending himself and quoting his high school resume. Think that went over well?
Along with being new, and getting out to as many scrimmages and practices as possible, you'll get feedback (solicited and unsolicited) from a variety of sources. Some of it will inevitably be conflicting, and it's unlikely you'll know who to listen to right from the start. When you're in those spots, listen politely, say thank you, and figure it out later. Find a mentor or someone you can trust and can talk to later to figure out where the truth lies.
When the season rolls around, hopefully you'll be evaluated in some of your games and/or have your film graded. Don't be scared of downgrades or afraid to make mistakes. The move from HS to college is an adjustment, you might have to fine-tune your interpretation of what constitutes a quality hold, or dpi, etc...but study and learn from those occasions so that you don't make the same mistakes again (goes back to being coachable).
Lastly, before this turns into rambling nonsense, be honest with yourself when it comes to self-evaluation. What we do requires a certain amount of ego, and the best officials walk the fine line between confidence and arrogance. But when the season wraps up, you'll have the potential to make real improvements if you can candidly identify the areas you need to work on. If it's rules, get in the book or find a learning strategy that fits you best. If it's fitness, make the commitment to get in the gym. If it's judgement, watch more film. If it's communication, there are books on strategies...these are simplified solutions and of course it's not quite that easy, but if you make a plan and stick to it you'll be ahead of most others.
Enjoy the ride, make some relationships along the way, and when the opportunity comes along where you can help out someone who is in the position you're in now, do it.